Miles per gallon gasoline equivalent

Monroney label showing the EPA's fuel economy equivalent ratings for the 2011 Chevrolet Volt. The rating for all-electric mode (left) is expressed in miles per gallon gasoline equivalent.

Miles per gallon gasoline equivalent (MPGe or MPG_ge) is a measure of the average distance traveled per unit of energy consumed. MPGe is used by the United States Environmental Protection Agency (EPA) to compare energy consumption of alternative fuel vehicles, plug-in electric vehicles and other advanced technology vehicles with the fuel economy of conventional internal combustion vehicles expressed as miles per US gallon.^[1][2]

The MPGe metric was introduced in November 2010 by EPA in the Monroney sticker of the Nissan Leaf electric car and the Chevrolet Volt plug-in hybrid. The ratings are based on EPA's formula, in which 33.7 kilowatt-hours (121 megajoules) of electricity is equivalent to one gallon of gasoline,^[3] and the energy consumption of each vehicle during EPA's five standard drive cycle tests simulating varying driving conditions.^[4][5] All new cars and light-duty trucks sold in the U.S. are required to have this label showing the EPA's estimate of fuel economy of the vehicle.^[2]

In a joint ruling issued in May 2011 the National Highway Traffic Safety Administration (NHTSA) and EPA established the new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year 2013. This ruling uses miles per gallon gasoline equivalent for all fuel and advanced technology vehicles available in the U.S. market including plug-in hybrids, electric vehicles, flexible-fuel vehicles, hydrogen fuel cell vehicle, natural gas vehicles, diesel-powered vehicles, and gasoline-powered vehicles.^[6][7] In addition to being displayed on new vehicles, fuel economy ratings are used by the U.S. Department of Energy (DOE) to publish the annual Fuel Economy Guide; the U.S. Department of Transportation (DOT) to administer the Corporate Average Fuel Economy (CAFE) program; and the Internal Revenue Service (IRS) to collect gas guzzler taxes.^[2]

Fuel economy estimates for window stickers and CAFE standard compliance are different. The EPA MPGe rating shown in the Monroney label is based on the consumption of the on-board energy content stored in the fuel tank or in the vehicle's battery, or any other energy source, and only represents the tank-to-wheel energy consumption. CAFE estimates are based on a well-to-wheel basis and in the case of liquid fuels and electric drive vehicles also account for the energy consumed upstream to produce the fuel or electricity and deliver it to the vehicle. Fuel economy for CAFE purposes include an incentive adjustment for alternative fuel vehicles and plug-in electric vehicles which results in higher MPGe than those estimated for window stickers.^[8][9]

Background

1988: Alternative Motor Fuels Act

The Alternative Motor Fuels Act (AMFA) enacted in 1988 provides Corporate Average Fuel Economy (CAFE) incentives for the manufacture of vehicles that use ethanol, methanol, or natural gas fuels, either powered exclusively on these alternative fuels or in conjunction with gasoline or diesel fuel, such flexible-fuel vehicles. In order to provide incentives for the widespread use of these fuels and to promote the production of alternative fuel vehicles, AMFA allows manufacturers producing alternative fuel vehicles to gain CAFE credits by manufacturing these vehicles, which allows them to raise their overall fleet fuel economy levels to comply with the CAFE standards until the established cap level.^[10][11]

Beginning in 1993, manufacturers of qualified alternative fuel vehicles can benefit for their CAFE estimation, by computing the weighted average of the fuel economy of the produced alternative fuel vehicles by dividing the alcohol fuel economy by a factor of 0.15. As an example, a dedicated alternative fuel vehicle that would achieve 15 mpg fuel economy while operating on alcohol would have a CAFE calculated as follows:^[11]

FE = (1/0.15)(15) = 100 miles per gallon

For alternative dual-fuel vehicles, an assumption is made that the vehicles would operate 50% of the time on the alternative fuel and 50% of the time on conventional fuel, resulting in a fuel economy that is based on a harmonic average of alternative fuel and conventional fuel. For example, for an alternative dual-fuel model that achieves 15 miles per gallon operating on an alcohol fuel and 25 mpg on the conventional fuel, the resulting CAFE would be:^[11]

FE = 1 / [(0.5/25) + (0.5/100)] = 40 miles per gallon

Calculation of fuel economy for natural gas vehicles is similar. For the purposes of this calculation, the fuel economy is equal to the weighted average of the fuel economy while operating on natural gas and while operating on either gasoline or diesel fuel. AMFA specifies the energy equivalency of 100 cubic feet of natural gas to be equal to 0.823 gallons of gasoline, with the gallon equivalency of natural gas to be considered to have a fuel content, similar to that for alcohol fuels, equal to 0.15 gallons of fuel. For example, under this conversion and gallon equivalency, a dedicated natural gas vehicle that achieves 25 miles per 100 cubic feet of natural gas would have a CAFE value as follows:^[11]

FE = (25/100) x (100/0.823)(1/0.15) = 203 miles per gallon

The Energy Policy Act of 1992 expanded the definition of alternative fuel to include liquefied petroleum gas, hydrogen, liquid fuels derived from coal and biological materials, electricity and any other fuel that the Secretary of Transportation determines to be substantially non-petroleum based and has environmental and energy security benefits. Beginning in 1993, manufacturers of these other alternative fuel automobiles that meet the qualifying requirements can also benefit for special treatment in the calculation of their CAFE.^[11]

1994: Gasoline gallon equivalent

In 1994 the U.S. National Institute of Standards and Technology (NIST) introduced gasoline gallon equivalent (GGE) as a metric for fuel economy for natural gas vehicles. NIST defined a gasoline gallon equivalent (GGE) as 5.660 pounds of natural gas, and gasoline liter equivalent (GLE) as 0.678 kilograms of natural gas.^[12]

2000: Petroleum-equivalent fuel economy

Energy efficiency for selected electric cars leased in California between 1996–2003
Vehicle	Model year	Type of battery	Energy use (Wh/mi)
GM EV1[13]	1997	Lead acid	164
GM EV1[14]	1999	NiMH	179
Toyota RAV4 EV[15]	1996	Lead acid	235
Toyota RAV4 EV[16]	2000	NiMH	400
Ford Ranger EV[17]	1998	Lead acid	337
Chevrolet S-10 EV[18]	1997	Lead acid	292

During the late 1990s and early 2000s several electric cars were produced in limited quantities as a result of the California Air Resources Board (CARB) mandate for more fuel-efficient zero-emissions vehicles. Popular models available in California included the General Motors EV1 and the Toyota RAV4 EV.^[19][20] The US DoE and EPA rating for on board energy efficiency for these electric vehicles was expressed as kilowatt-hour/mile (KWh/mi), the most commonly known metric in science and engineering for measuring energy consumption, and used as the billing unit for energy delivered to consumers by electric utilities.^[21]

In order to address the Corporate Average Fuel Economy (CAFE) regulations mandated by the US Congress in 1975, the U.S. Department of Energy established in July 2000 a methodology for calculating the petroleum-equivalent fuel economy of electric vehicles on a well-to-wheel basis. The methodology considers the upstream efficiency of the processes involved in the two fuel cycles, including efficiency factors for petroleum refining and distribution, as well as the national average efficiency for electricity generation and transmission.^[9] The formula also includes a fuel efficiency incentive factor of 1/0.15 to benefit electric vehicles. This reward factor is intended provide an incentive for vehicle manufactures to produce and sell electric vehicles, as a higher equivalent fuel economy for EVs improves the carmaker overall fleet fuel economy levels in complying with the CAFE standards, and Congress anticipated that such an incentive would help accelerate the commercialization of electric vehicles. The incentive factor chosen by DoE for EVs is the same 1/0.15 factor already applied in the regulatory treatment of other types of alternative fuel vehicles.^[9] When all factors are considered in DoE's formula, the energy efficiency or equivalent fuel economy of electric vehicles increases from 33,705 Wh/gallon (plug-to-wheel) to 82,049 Wh/gallon (well-to-wheel).^[21]

2007: X Prize

In April 2007, as part of Draft Competition Guidelines released at the New York Auto Show, MPGe was announced as the main merit metric for the Progressive Insurance Automotive X Prize, a competition developed by the X Prize Foundation for super-efficient vehicles that can achieve at least 100 MPGe.^[22] In February 2009, Consumer Reports announced that, as part of a partnership with the X Prize Foundation, they planned to report MPGe as one of several measures that will help consumers understand and compare vehicle efficiency for alternative fuel vehicles.^[23]

2010–2011: Miles per gallon equivalent

Old Monroney label for electric cars showing in prominent larger font the fuel economy rating in KW-hr/100 miles for the 2009 Mini E.

New Monroney label for electric cars showing in prominent larger font the fuel economy rating in miles per gallon gasoline equivalent for the 2011 Nissan Leaf. The rating in KW-hr/100 miles is shown below MPG-e in smaller font.

As required by the 2007 Energy Independence and Security Act (EISA), with the introduction of advanced-technology vehicles in the U.S. new information should be incorporated in the Monroney label of new cars and light-duty trucks sold in the country, such as ratings on fuel economy, greenhouse gas emissions, and other air pollutants. The U.S. Environmental Protection Agency and the National Highway Traffic Safety Administration (NHTSA) have conducted a series of studies to determine the best way to redesign this label to provide consumers with simple energy and environmental comparisons across all vehicles types, including battery electric vehicles (BEV), plug-in hybrid electric vehicles (PHEV), and conventional internal combustion engine vehicles powered by gasoline and diesel, in order to help consumers choose more efficient and environmentally friendly vehicles. These changes were proposed to be introduced in new vehicles beginning with model year 2012.^[2][24]

The EPA rating for on board energy efficiency for electric vehicles before 2010 was expressed as kilowatt-hour per 100 miles (kW-hrs/100 mi).^[21][25] The window sticker of the 2009 Mini E showed an energy consumption of 33 kW-hrs/100 mi for city driving and 36 kW-hrs/100 mi on the highway, technically equivalent to 102 mpg city and 94 mpg highway.^[25] The 2009 Tesla Roadster was rated 32 kW-hrs/100 mi in city and 33 kW-hrs/100 mi on the highway, equivalent to 105 mpg city and 102 mpg highway.^[26][27]

As part of the research and redesign process, EPA conducted focus groups where participants were presented with several options to express the consumption of electricity for plug-in electric vehicles. The research showed that participants did not understand the concept of a kilowatt hour as a measure of electric energy use despite the use of this unit in their monthly electric bills. Instead, participants favored a miles per gallon equivalent, MPGe, as the metric to compare with the familiar miles per gallon used for gasoline vehicles. The research also concluded that the kW-hrs per 100 miles metric was more confusing to focus group participants compared to a miles per kW-hr. Based on these results, EPA decided to use the following fuel economy and fuel consumption metrics on the redesigned labels: MPG (city and highway, and combined); MPGe (city and highway, and combined); Gallons per 100 miles; kW-hrs per 100 miles.^[24]

The proposed design and final content for two options of the new sticker label that would be introduced in 2013 model year cars and trucks were consulted for 60 days with the public in 2010, and both include miles per gallon equivalent and kW-hrs per 100 miles as the fuel economy metrics for plug-in cars, but in one option MPGe and annual electricity cost are the two most prominent metrics.^[28][29] In November 2010, EPA introduced MPGe as comparison metric on its new sticker for fuel economy for the Nissan Leaf and the Chevrolet Volt.^[4][5]

Typical label for hydrogen fuel cell vehicles expressed in MPGe, mandatory starting with 2013 model year.

In May 2011, the National Highway Traffic Safety Administration (NHTSA) and EPA issued a joint final rule establishing new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year 2013. The ruling includes new labels for alternative fuel and alternative propulsion vehicles available in the US market, such as plug-in hybrids, electric vehicles, flexible-fuel vehicles, hydrogen fuel cell vehicle, and natural gas vehicles.^[6][7] The common fuel economy metric adopted to allow the comparison of alternative fuel and advanced technology vehicles with conventional internal combustion engine vehicles is miles per gallon of gasoline equivalent (MPGe). A gallon of gasoline equivalent means the number of kilowatt-hours of electricity, cubic feet of compressed natural gas (CNG), or kilograms of hydrogen that is equal to the energy in a gallon of gasoline.^[6]

The new labels also show for the first time an estimate of how much fuel or electricity it takes to drive 100 miles (160 km), introducing to U.S. consumers with fuel consumption per distance traveled, the metric commonly used in many other countries. EPA explained that the objective is to avoid the traditional miles per gallon metric that can be potentially misleading when consumers compare fuel economy improvements, and known as the "MPG illusion."^[6]

Description

The miles per gallon gasoline equivalent is based on the energy content of gasoline. The energy obtainable from burning one US gallon of gasoline is 115,000 BTU or 33.70 kWh.^[3]

To convert the mile per gallon rating into other units of distance per unit energy used, the mile per gallon value can be multiplied by one of the following factors to obtain other units:

1 MPGe	≈ 1 mile/ per 33.70 kW·h
	≈ 8.696 miles/ million BTU
	≈ 0.02967 miles/kW·h
	≈ 0.04775 km/kW·h
	≈ 0.013 km/MJ

Conversion to MPGe

MPGe is determined by converting the vehicle consumption per unit distance, as determined through computer modeling or completion of an actual driving cycle, from its native units into a gasoline energy equivalent. Examples of native units include W·h for electric vehicles, kg-H2 for hydrogen vehicles, gallons for biodiesel or liquefied natural gas vehicles, cubic feet for compressed natural gas vehicles, and pounds for propane or Liquefied petroleum gas vehicles. Special cases for specific alternative fuels are discussed below, but a general formula for MPGe is:

$MPGe = \frac{total~miles~driven}{\left [ \frac{total~energy~of~all~fuels~consumed}{energy~of~one~gallon~of~gasoline} \right ]} = \frac{(total\ miles\ driven) \times (energy\ of\ one\ gallon\ of\ gasoline)} {total~energy~of~all~fuels~consumed}$

For EPA, this considers the tank-to-wheel for liquids and wall-to-wheel energy consumption for electricity, i.e. it measures the energy for which the owner usually pays. For EVs the energy cost includes the conversions from AC to charge the battery.^[30] The EPA MPGe ratings displayed in window stickers do not account for the energy consumption upstream, which includes the energy or fuel required to generate the electricity or to extract and produce the liquid fuel; the energy losses due to power transmission; or the energy consumed for the transportation of the fuel from the well to the station.^[9][31]

Basic values for the energy content of various fuels are given by the defaults used in the Department of Energy GREET (Greenhouse gases, Regulated Emissions, and Energy used in Transportation) model,^[32] as follows:

Note: 1 kWh is equivalent to 3,412 BTU

Fuel	Unit	Btu/Unit	kWh/Unit
gasoline	gallon	116,090	34.02
diesel	gallon	129,488	37.95
biodiesel	gallon	119,550	35.04
ethanol	gallon	76,330	22.37
E85	gallon	82,000	24.03
CNG	100 SCF	98,300	28.81
H2-Gas	100 SCF	28,900	8.47
H2-Liq	gallon	30,500	8.94
LPG	gallon	84,950	24.9
methanol	gallon	57,250	16.78

The energy content of a particular fuel can vary somewhat given its specific chemistry and production method. For example, in the new efficiency ratings that have been developed by the United States Environmental Protection Agency (EPA) for battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs) – see below – the energy content of a gallon of gasoline is assumed to be 114,989.12 BTU or 33.7 kWh.^[3]

Electric and plug-in hybrid electric vehicles

Monroney label showing the EPA's fuel economy equivalent ratings for the 2011 Smart ED electric car.

Between 2008 and 2010 several major automakers began commercializing battery electric vehicles (BEVs), which are powered exclusively on electricity, and plug-in hybrid electric vehicles (PHEVs), which use electricity together with a liquid fuel stored in an on-board fuel tank, usually gasoline, but it might be also powered by diesel, ethanol, or flex-fuel engines.

For battery electric vehicles, the U.S. Environmental Protection Agencys formula to calculate the battery-to wheel MPGe is based on energy standards established by the U.S. Department of Energy in 2000:^[1][8][9]

$MPGe = \frac { E_G} {E_M*E_E} = \frac{ 33,705 } {E_M}$

where

$MPGe$ is expressed as miles per gallon gasoline equivalent (as shown in the Monroney label)

$E_G =$ energy content per gallon of gasoline = 115,000 BTUs/gallon, as set by U.S. DoE and reported by the Alternative Fuel Data Center.^[9]

$E_M =$ wall-to-wheel electrical energy consumed per mile (Wh/mi) as measured through EPA's five standard drive cycle tests for electric cars and SAE test procedures^[8][30]

$E_E =$ energy per KWatt-hour of electricity (BTU/Wh) = 3.412^[9]

The formula employed by the EPA for calculating their rated MPGe does not account for any fuel or energy consumed upstream such as the generation and transmission of electrical power, or well-to-wheel life cycle, as EPA's comparison with internal combustion vehicles is made on a tank-to-wheel versus battery-to wheel basis.

The California Air Resources Board uses a different dynamometer testing than EPA, and considers reformulated gasoline sold in that state. For CARB estimates the formula becomes:^[8]

$MPGe = \frac { E_G} {E_M*E_E} = \frac{ 32,600 } {E_M}$

The new SAE J1711 standard for measuring the exhaust emissions and fuel economy of hybrid electric vehicles and plug-in hybrids was approved in July 2010. The recommended procedures for PHEVs were revised at Argonne National Laboratory, and EPA's new regulation to define PHEV fuel economy reporting protocol is expected to be based on SAE J1711.^[33][34] In November 2010 EPA decided to rate electric mode and gasoline only mode separately, and these are the two figures prominently displayed in the window sticker of the 2011 Chevrolet Volt. In electric mode the Volt's rating is estimated with the same formula as an electric car.^[5][8] The overall or composite fuel economy rating combining electricity and gasoline powered are displayed in the Monroney label in a much smaller type, and as part of the comparison of the Volt's fuel economy among all vehicles and within compact cars.^[35] EPA has considered several methodologies for rating the overall fuel economy of PHEVs, but as of February 2011 EPA has not announced the final methodology that will be applied for the purposes of estimating the new manufacture's 2012-2016 Corporate Average Fuel Economy (CAFE) credits for plug-in hybrids.^[8][36]

Examples

In November 2010 the EPA began including "MPGe" in its new sticker for fuel economy and environmental comparisons. The EPA rated the Nissan Leaf electric car with a combined fuel economy of 99 MPGe,^[4] and rated the Chevrolet Volt plug-in hybrid with a combined fuel economy of 93 MPGe in all-electric mode, 37 MPG when operating with gasoline only, and an overall fuel economy rating of 60 mpg-US (3.9 L/100 km) combining power from electricity and gasoline.^[5][35][37] For both vehicles EPA calculated the MPGe rating under its five-cycle tests using the formula displayed earlier with a conversion factor of 33.7 kW-hr of electricity being the energy equivalent of a gallon of gasoline.^[5]

All-electric cars

The following table compares out-of-pocket fuel costs estimated by the U.S. Environmental Protection Agency according to its official ratings for fuel economy (miles per gallon gasoline equivalent in the case of plug-in electric vehicles) for series production all-electric passenger vehicles rated by the EPA as of December 2015,^[38] versus EPA rated most fuel efficient plug-in hybrid with long distance range (Chevrolet Volt - second generation ), gasoline-electric hybrid car (Toyota Prius Eco - fourth generation),^[39][40][41] and EPA's average new 2016 vehicle, which has a fuel economy of 25 mpg_-US (9.4 L/100 km; 30 mpg_-imp).^[38][39]

Comparison of fuel efficiency and costs for all the electric cars rated by the EPA for the U.S. market as of December 2015 against EPA rated most fuel efficient plug-in hybrid, hybrid electric vehicle and 2016 average gasoline-powered car in the U.S. (Fuel economy and operating costs as displayed in the Monroney label)[38][42]
Vehicle	Model year	EPA rated Combined fuel economy	EPA rated City fuel economy	EPA rated Highway fuel economy	Cost to drive 25 miles (40 km)	Annual fuel cost	Notes
BMW i3[43]	2014/15	124 mpg-e (27 kW·h/100 mi 17.2 kW·h/100 km)	137 mpg-e (25 kW·h/100 mi 15.6 kW·h/100 km)	111 mpg-e (30 kW·h/100 mi 19.3 kW·h/100 km)	$0.91	$550	(1) (3) (4) (5)
Scion iQ EV[44]	2013	121 mpg-e (28 kW·h/100 mi 17.7 kW·h/100 km)	138 mpg-e (24 kW·h/100 mi 15.5 kW·h/100 km)	105 mpg-e (32 kW·h/100 mi 20.4 kW·h/100 km)	$0.91	$550	(1)
Chevrolet Spark EV[45]	2014/15/16	119 mpg-e (28 kW·h/100 mi 18.0 kW·h/100 km)	128 mpg-e (26 kW·h/100 mi 16.7 kW·h/100 km)	109 mpg-e (31 kW·h/100 mi 19.6 kW·h/100 km)	$0.91	$550	(1)
Honda Fit EV[46]	2013/14	118 mpg-e (29 kW·h/100 mi 18.1 kW·h/100 km)	132 mpg-e (26 kW·h/100 mi 16.2 kW·h/100 km)	105 mpg-e (32 kW·h/100 mi 20.4 kW·h/100 km)	$0.94	$550	(1)
Fiat 500e[47]	2013/14/15	116 mpg-e (29 kW·h/100 mi 18.4 kW·h/100 km)	122 mpg-e (28 kW·h/100 mi 17.5 kW·h/100 km)	108 mpg-e (31 kW·h/100 mi 19.8 kW·h/100 km)	$0.95	$550	(1)
Volkswagen e-Golf[48]	2015/16	116 mpg-e (29 kW·h/100 mi 18.4 kW·h/100 km)	126 mpg-e (27 kW·h/100 mi; 17.0 kW·h/100 km)	105 mpg-e (33 kW·h/100 mi; 20.4 kW·h/100 km)	$0.95	$550	(1)
Nissan Leaf (24 kW-hr)[49]	2013/14/15/16	114 mpg-e (30 kW·h/100 mi; 18.7 kW·h/100 km)	126 mpg-e (27 kW·h/100 mi; 17.0 kW·h/100 km)	101 mpg-e (33 kW·h/100 mi; 21 kW·h/100 km)	$0.96	$600	(1) (6)
Mitsubishi i[50]	2012/13/14/16	112 mpg-e (30 kW·h/100 mi; 19.1 kW·h/100 km)	126 mpg-e (27 kW·h/100 mi; 17.0 kW·h/100 km)	99 mpg-e (34 kW·h/100 mi; 22 kW·h/100 km)	$0.98	$600	(1)
Nissan Leaf (30 kW-hr)[49]	2016	112 mpg-e (30 kW·h/100 mi; 19.1 kW·h/100 km)	124 mpg-e (28 kW·h/100 mi; 17.2 kW·h/100 km)	101 mpg-e (34 kW·h/100 mi; 21 kW·h/100 km)	$0.97	$600	(1)
Fiat 500e[51]	2016	112 mpg-e (30 kW·h/100 mi; 19.1 kW·h/100 km)	121 mpg-e (28 kW·h/100 mi; 17.7 kW·h/100 km)	103 mpg-e (33 kW·h/100 mi; 21 kW·h/100 km)	$0.97	$600	(1)
Smart electric drive[52]	2013/14/15/16	107 mpg-e (32 kW·h/100 mi; 20.0 kW·h/100 km)	122 mpg-e (28 kW·h/100 mi; 17.5 kW·h/100 km)	93 mpg-e (36 kW·h/100 mi; 23 kW·h/100 km)	$1.02	$600	(1) (7)
Kia Soul EV[53]	2015/16	105 mpg-e (32 kW·h/100 mi; 20.4 kW·h/100 km)	120 mpg-e (29 kW·h/100 mi; 18 kW·h/100 km)	92 mpg-e (37 kW·h/100 mi; 23 kW·h/100 km)	$1.04	$600	(1)
Ford Focus Electric[54]	2012/13/14/15/16	105 mpg-e (32 kW·h/100 mi; 20.4 kW·h/100 km)	110 mpg-e (31 kW·h/100 mi; 19 kW·h/100 km)	99 mpg-e (34 kW·h/100 mi; 22 kW·h/100 km)	$1.04	$600	(1)
Tesla Model S AWD - 70D[38][55]	2015/16	101 mpg-e (33 kW·h/100 mi; 21 kW·h/100 km)	101 mpg-e (33 kW·h/100 mi; 21 kW·h/100 km)	102 mpg-e (33 kW·h/100 mi; 21 kW·h/100 km)	$1.07	$650	(1)
Tesla Model S AWD - 85D[38][56]	2015/16	100 mpg-e (34 kW·h/100 mi; 21 kW·h/100 km)	95 mpg-e (35 kW·h/100 mi; 22 kW·h/100 km)	106 mpg-e (32 kW·h/100 mi; 20.2 kWh/100 km)	$1.10	$650	(1) (8)
Tesla Model S AWD - 90D[38][55]	2015/16	100 mpg-e (34 kW·h/100 mi; 21 kW·h/100 km)	95 mpg-e (35 kW·h/100 mi; 22 kW·h/100 km)	106 mpg-e (32 kW·h/100 mi; 20.2 kW·h/100 km)	$1.10	$650	(1)
Tesla Model S (60 kW·h)[38][55]	2014/15/16	95 mpg-e (35 kW·h/100 mi; 22 kW·h/100 km)	94 mpg-e (36 kW·h/100 mi; 23 kW·h/100 km)	97 mpg-e (35 kW·h/100 mi; 22 kW·h/100 km)	$1.14	$700	(1)
Tesla Model S AWD - P85D[38][56]	2015/16	93 mpg-e (36 kW·h/100 mi; 23 kW·h/100 km)	89 mpg-e (38 kW·h/100 mi; 24 kW·h/100 km)	98 mpg-e (35 kW·h/100 mi; 22 kW·h/100 km)	$1.17	$700	(1) (8)
Tesla Model S AWD - P90D[38][55]	2015/16	93 mpg-e (36 kW·h/100 mi; 23 kW·h/100 km)	89 mpg-e (38 kW·h/100 mi; 24 kW·h/100 km)	98 mpg-e (35 kW·h/100 mi; 22 kW·h/100 km)	$1.17	$700	(1)
Tesla Model X AWD – 90D[57]	2016	92 mpg-e (34 kW·h/100 mi; 23 kW·h/100 km)	90 mpg-e (37 kW·h/100 mi; 24 kW·h/100 km)	94 mpg-e (32 kW·h/100 mi; 23 kW·h/100 km)	$1.20	$700	(1)
Tesla Model X AWD – P90D[57]	2016	89 mpg-e (38 kW·h/100 mi; 24 kW·h/100 km)	89 mpg-e (38 kW·h/100 mi; 24 kW·h/100 km)	90 mpg-e (38 kW·h/100 mi; 24 kW·h/100 km)	$1.23	$750	(1)
Tesla Model S (85 kW·h)[58]	2012/13/14/15	89 mpg-e (38 kW·h/100 mi; 24 kW·h/100 km)	88 mpg-e (38 kW·h/100 mi; 24 kW·h/100 km)	90 mpg-e (37 kW·h/100 mi; 24 kW·h/100 km)	$1.23	$750	(1)
Mercedes-Benz B-Class Electric Drive[59]	2014/15/16	84 mpg-e (40 kW·h/100 mi; 25 kW·h/100 km)	85 mpg-e (40 kW·h/100 mi; 25 kW·h/100 km)	83 mpg-e (41 kW·h/100 mi; 26 kW·h/100 km)	$1.30	$800	(1)
Toyota RAV4 EV[60]	2012/13/14	76 mpg-e (44 kW·h/100 mi; 28 kW·h/100 km)	78 mpg-e (43 kW·h/100 mi; 27 kW·h/100 km)	74 mpg-e (46 kW·h/100 mi; 29 kW·h/100 km)	$1.43	$850	(1)
BYD e6[38][61]	2012/13/14/15/16	63 mpg-e (54 kW·h/100 mi; 34 kW·h/100 km)	61 mpg-e (55 kW·h/100 mi; 35 kW·h/100 km)	65 mpg-e (52 kW·h/100 mi; 33 kW·h/100 km)	$1.76	$1,050	(1)
Second gen Chevrolet Volt[38][62][63] Plug-in hybrid (PHEV) Electricity only/ gasoline only	2016	106 mpg-e (31 kW·h/100 mi; 20.2 kW·h/100 km) 42 mpg	113 mpg-e (30 kW·h/100 mi; 18.9 kW·h/100 km) 43 mpg	99 mpg-e (35 kW·h/100 mi; 22 kW·h/100 km) 42 mpg	$1.01/$1.23	$650	(1) (2) (9)
2016 Toyota Prius Eco (4th gen)[40] Hybrid electric vehicle (HEV) Gasoline-electric hybrid	2016	56 mpg	58 mpg	53 mpg	$0.92	$550	(2) (10)
Ford Fusion AWD A-S6 2.0L[38][64] Gasoline-powered (Average new vehicle)	2016	25 mpg	22 mpg	31 mpg	$2.06	$1,250	(2) (11)
Notes: All estimated fuel costs based on 15,000 miles (24,000 km) annual driving, 45% highway and 55% city (1) Values rounded to the nearest $50. Electricity cost of $0.13/kW·h (as of 3 December 2015). Conversion 1 gallon of gasoline=33.7 kW·h. (2) Regular gasoline price of US$2.06 per gallon (as of 3 December 2015). (3) The 2014 i3 REx is classified by EPA as a series plug-in hybrid, while for CARB is a range-extended battery-electric vehicle (BEVx). The i3 REx is the most fuel efficient EPA-certified current year vehicle with a gasoline engine with a combined gasoline/electricity rating of 88 mpg-e, but its total range is limited to 150 mi (240 km).[39][65] (4) The 2014 BMW i3 is the most fuel efficient EPA-certified vehicle of all fuel types considered in all years.[65] (5) The i3 REx has a combined fuel economy in all-electric mode of 117 mpg-e (29 kW·h/100 mi; 18 kW·h/100 km).[66] (6)The 2016 model year Leaf correspond to the variant with the 24 kW·h battery pack. (7) Ratings correspond to both convertible and coupe models. (8) Model with 85 kW·h battery pack (9) Most fuel efficient plug-in hybrid capable of long distance travel. The 2016 Volt has a rating of 77 mpg-e for combined gasoline/electricity operation.[39] (10) Most fuel efficient hybrid electric car.[38][39] (11) Other 2016 MY cars achieving 25 mpg-US (9.4 L/100 km; 30 mpg-imp) combined city/hwy include the Honda Accord A-S6 3.5L, Toyota Camry A-S6 3.5L and Toyota RAV4 A-S6 2.5L.[38][64]

Plug-in hybrids

The following table compares EPA's estimated out-of-pocket fuel costs and fuel economy ratings of serial production plug-in hybrid electric vehicles rated by EPA as of March 2016 expressed in miles per gallon gasoline equivalent (mpg-e),^[38] versus the most fuel efficient gasoline-electric hybrid car, the 2016 Toyota Prius Eco (fourth generation), rated 56 mpg_-US (4.2 L/100 km; 67 mpg_-imp), and EPA's average new 2016 vehicle, which has a fuel economy of 25 mpg_-US (9.4 L/100 km; 30 mpg_-imp).^[38][67][40] The table also shows the fuel efficiency for plug-in hybrids in all-electric mode expressed as KWh/100 mile, the metric used by EPA to rate electric cars before November 2010.^[21]

Comparison of out-of-pocket fuel costs and fuel economy for plug-in hybrid electric cars rated by EPA as of March 2016 with MPGe and conventional MPG^(1) (as displayed in the Monroney label and the US DoE fueleconomy.gov website)
Vehicle	Year model	Operating mode (EV range)	EPA rated Combined fuel economy	EPA rated city fuel economy	EPA rated highway fuel economy	Fuel cost to drive 25 miles	Annual fuel cost^(1) (15,000 mi)	Notes
BMW i3 REx[68][69]	2014/15	Electricity only (72 mi)	117 mpg-e (29 kWh/100 mi)	97 mpg-e (35 kW·h/100 mi)	79 mpg-e (44 kW·h/100 mi)	$0.94	$650	The EPA classifies the i3 REx as a series plug-in hybrid while CARB as a range-extended battery-electric vehicle (BEVx). The 2014 i3 REx is the most fuel efficient EPA-certified current year vehicle with a gasoline engine with a combined gasoline/electricity rating of 88 mpg-e (city 97 mpg-e/hwy 79 mpg-e).[70][71]
		Gasoline only (78 mi)	39 mpg	41 mpg	37 mpg	$1.61
Honda Accord Plug-in Hybrid[72]	2014	Electricity and gasoline (13 mi)	115mpg-e (29 kWh/100 mi)	-	-	$1.03	$650	The 2014 Accord is the most fuel efficient plug-in hybrid in blended EV mode with a rating of 115 mpg-e. The Accord has a rating for combined EV/hybrid operation of 57 mpg-e.[73]
		Gasoline only	46 mpg	47 mpg	46 mpg	$1.11
Chevrolet Volt (2nd gen)[74][75]	2016/17	Electricity only (53 mi)	106 mpg-e (31 kWh/100 mi)	113 mpg-e (29 kWh/100 mi)	99 mpg-e (34 kWh/100 mi)	$1.01	$650	The 2016 Volt has a combined gasoline/electricity rating of 77 mpg-e (city 82 mpg-e/hwy 72 mpg-e).[70] Regular gasoline.
		Gasoline only	42 mpg	43 mpg	42 mpg	$1.21
Hyundai Sonata PHEV[76]	2016	Electricity and gasoline (27 mi)	99mpg-e (34 kWh/100 mi)	-	-	$1.19	$700	During the first 27 mi uses some gasoline. The actual all-electric range is between 0 to 27 mi.[76]
		Gasoline only	40 mpg	-	-	$1.28
Chevrolet Volt (1st gen)[77][78]	2013/15	Electricity only (38 mi)	98 mpg-e (35 kWh/100 mi)	-	-	$1.14	$800	The 2013/15 Volt has a combined gasoline/electricity rating of 62 mpg-e (city 63 mpg-e/hwy 61 mpg-e).[70] Premium gasoline.
		Gasoline only	37 mpg	35 mpg	40 mpg	$1.70
Toyota Prius PHV[79]	2012/15	Electricity and gasoline (11 mi)	95 mpg-e (29 kWh/100 mi plus 0.2 gallons/100 mi)	-	-	$1.03	$600	After the first 11 miles the car functions like a regular Prius hybrid The 2012/15 Prius has a combined gasoline/electricity rating of 58 mpg-e (city 59 mpg-e/hwy 56 mpg-e).[70]
		Gasoline only	50 mpg	51 mpg	49 mpg	$1.02
Chevrolet Volt[80]	2011/12	Electricity only	94 mpg-e (36 kWh/100 mi)	95 mpg-e (36 kWh/100 mi)	93 mpg-e (37 kWh/100 mi)	$1.17	$800	Premium gasoline.
		Gasoline only	37 mpg	35 mpg	40 mpg	$1.70
Ford C-Max Energi[81] Ford Fusion Energi[81]	2013/16	Electricity and gasoline (20 mi)	88 mpg-e (37 kWh/100 mi)	95 mpg-e (36 kW·h/100 mi)	81 mpg-e (42 kW·h/100 mi)	$1.25	$750	The Energi did not use any gasoline for the first 20 miles in EPA tests, but depending on the driving style, the car may use both gasoline and electricity during EV mode. The Energi models have a combined EV/hybrid operation rating of 51 mpg-e (city 55 mpg-e/hwy 46 mpg-e).[70]
		Gasoline only	38 mpg	40 mpg	36 mpg	$1.34
Audi A3 e-tron ultra[82]	2016	Electricity only (17 mi)	86 mpg-e (38 kWh/100 mi)	-	-	$1.37	$900	During the first 17 mi uses some gasoline. The actual all-electric range is between 0 to 17 mi.[82]
		Gasoline only	39 mpg	-	-	$1.61
Cadillac ELR[83]	2014/15	Electricity only (37 mi)	82 mpg-e (41 kWh/100 mi)	-	-	$1.33	$900	The 2014/15 ELR has a combined gasoline/electricity rating of 54 mpg-e (city 54 mpg-e/hwy 55 mpg-e).[70]
		Gasoline only	33 mpg	31 mpg	35 mpg	$1.90
Audi A3 e-tron[82]	2016	Electricity only (16 mi)	83 mpg-e (40 kWh/100 mi)	-	-	$1.49	$950	During the first 16 mi uses some gasoline. The actual all-electric range is between 0 to 16 mi.[82]
		Gasoline only	35 mpg	-	-	$1.79
BMW i8[68][84]	2014/15/16	Electricity and gasoline (15 mi)	76 mpg-e (43 kWh/100 mi)	-	-	$1.77	$1,150	The i8 does not run on 100% electricity as it consumes 0.1 gallons per 100 mi in EV mode (all-electric range = 0 mi) The i8 has a rating for combined EV/hybrid operation of 37 mpg-e.[73]
		Gasoline only	28 mpg	28 mpg	29 mpg	$2.24
BMW 330e[85]	2016	Electricity and gasoline (14 mi)	72 mpg-e (47 kWh/100 mi)	-	-	$1.74	$1,050	During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 14 mi.[85] Premium gasoline.
		Gasoline only	31 mpg	-	-	$2.02
Porsche 918 Spyder[68][86]	2015	Electricity only (12 mi)	67 mpg-e (50 kWh/100 mi)	-	-	$1.62	$1,500	Premium gasoline.
		Gasoline only	22 mpg	20 mpg	24 mpg	$2.85
BMW X5 xDrive40e[87]	2016	Electricity only (14 mi)	56 mpg-e (59 kWh/100 mi)	-	-	$2.23	$1,450	During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 14 mi.[87]
		Gasoline only	24 mpg	-	-	$2.61
Mercedes-Benz S 500 e[88]	2015	Electricity and gasoline (14 mi)	58 mpg-e (59 kWh/100 mi)	-	-	$2.13	$1,350	During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 12 mi.[88] Premium gasoline.
		Gasoline only	26 mpg	-	-	$2.41
Fisker Karma[89]	2012	Electricity only (33 mi)	54 mpg-e (62 kWh/100 mi)	-	-	$2.02	$1,450	Premium gasoline.
		Gasoline only	20 mpg	20 mpg	21 mpg	$3.14
Volvo XC90 T8[90]	2016	Electricity and gasoline (14 mi)	53 mpg-e (58 kWh/100 mi)	-	-	$2.19	$1,400	During the first 14 mi uses some gasoline. The actual all-electric range is between 0 to 13 mi.[90] Premium gasoline.
		Gasoline only	25 mpg	-	-	$2.51
Porsche Panamera S E-Hybrid[91]	2016	Electricity and gasoline (16 mi)	51 mpg-e (51 kWh/100 mi)	-	-	$2.15	$1,350	The all-electric range is between 0 to 15 mi Premium gasoline.
		Gasoline only	25 mpg	23 mpg	29 mpg	$2.51
Porsche Panamera S E-Hybrid[91]	2014/15	Electricity and gasoline (16 mi)	50 mpg-e (52 kWh/100 mi)	-	-	$2.18	$1,400	The all-electric range is between 0 to 15 mi The S E-Hybrid has a rating for combined EV/hybrid operation of 31 mpg-e.[73]
		Gasoline only	25 mpg	23 mpg	29 mpg	$2.51
Porsche Cayenne S E-Hybrid[68][92]	2015/16	Electricity and gasoline (14 mi)	47 mpg-e (69 kWh/100 mi)	-	-	$2.24	$1,550	Premium gasoline.
		Gasoline only	22 mpg	21 mpg	24 mpg	$2.85
McLaren P1[68][93]	2014/15	Electricity and gasoline (19 mi)	18 mpg-e (25 kWh/100 mi)	-	-	$3.79	$2,200	The P1 does not run on 100% electricity as it consumes 4.8 gallons per 100 mi in EV mode (all-electric range = 0 mi)[93] The P1 has a rating for combined EV/hybrid operation of 17 mpg-e.[73]
		Gasoline only	17 mpg	16 mpg	20 mpg	$3.69
2016 Toyota Prius Eco (4th gen)[40]	2016	Gasoline-electric hybrid	56 mpg	58 mpg	53 mpg	$0.91	$550	Most fuel efficient hybrid electric car.[38]
Ford Fusion AWD 2.0L[38][64] (Average new vehicle)	2016	Gasoline only	25 mpg	22 mpg	31 mpg	$2.04	$1,200	Other 2016 MY cars achieving 25 mpg combined city/hwy include the Honda Accord 3.5L, Toyota Camry 3.5L and Toyota RAV4 2.5L.[38][64]
Notes: (1) Based on 45% highway and 55% city driving. Electricity cost of US$0.13/kWh, premium gasoline price of US$2.51 per gallon (used by the 2015 Volt, i3 REx, ELR, i8, Mercedes S500e, Karma and all Porsche models), and regular gasoline price of US$2.04 per gallon (as of 18 December 2015). Conversion 1 gallon of gasoline=33.7 kWh.

Fuel cell vehicles

The following table compares EPA's fuel economy expressed in miles per gallon gasoline equivalent (MPGe) for the three hydrogen fuel cell vehicles rated by the EPA as of June 2015, and available only in California.^[94][95]

Comparison of fuel economy expressed in MPGe for hydrogen fuel cell vehicles available for leasing in California and rated by the U.S. Environmental Protection Agency as of August 2015[94]
Vehicle		Model year	Combined fuel economy	City fuel economy	Highway fuel economy	Range	Annual fuel cost
Honda FCX Clarity		2014	59 mpg-e	58 mpg-e	60 mpg-e	231 mi (372 km)	NA
Hyundai Tucson Fuel Cell		2016	50 mpg-e	49 mpg-e	51 mpg-e	265 mi (426 km)	US$1,700
Toyota Mirai		2016	66 mpg-e	66 mpg-e	66 mpg-e	312 mi (502 km)	US$1,250
Notes: One kg of hydrogen is roughly equivalent to one U.S. gallon of gasoline.

Conversion using GGE

The same method can be applied to any other alternative fuel vehicle when that vehicle's energy consumption is known. Generally the energy consumption of the vehicle is expressed in units other than W·h/mile, or Btu/mile so additional arithmetic is required to convert to a gasoline gallon equivalent (GGE), using 33.7 kWh / gallon = 114989.17 btu / gallon. ^[3]

Hydrogen example with GGE

The 2008 Honda FCX Clarity is advertised to have a vehicle consumption of 72 mi/kg-H
2.^[96] Hydrogen has an energy density of 120 MJ/kg (113,738 BTU/kg),^[97] by converting this energy density to a GGE, it is found that 1.012 kg of hydrogen is needed to meet the equivalent energy of one gallon of gasoline. This conversion factor can now be used to calculate the MPGe for this vehicle.

$MPGe =MPkg_{H_2} \times {GGE}$,

$MPGe = 72 \frac{mi}{kg_{H_2}} \times {1.012 \frac{kg_{H_2}}{gallon_{gasoline}}} = 72.8 MPGe$

Life cycle assessment

Pump/Well-to-wheel

EPA's miles per gallon equivalent metric shown in the window sticker does not measure a vehicle's full cycle energy efficiency or well-to-wheel life cycle. Rather, the EPA presents MPGe in the same manner as MPG for conventional internal combustion engine vehicles as displayed in the Monroney sticker, and in both cases the rating only considers the pump-to-wheel or wall-to-wheel energy consumption, i.e. it measures the energy for which the owner usually pays. For EVs the energy cost includes the conversions from AC from the wall used to charge the battery^[30] The EPA ratings displayed in window stickers do not account for the energy consumption upstream, which includes the energy or fuel required to generate the electricity or to extract and produce the liquid fuel; the energy losses due to power transmission; or the energy consumed for the transportation of the fuel from the well to the station.^[9][31]

Petroleum-equivalency factor (PEF) — a CAFE metric

In 2000 the United States Department of Energy (DOE) established the methodology for calculating the petroleum-equivalent fuel economy of electric vehicles based on the well-to-wheel (WTW) gasoline-equivalent energy content of electricity (Eg). The methodology considers the upstream efficiency of the processes involved in the two fuel cycles, and considers the national average electricity generation and transmission efficiencies because a battery electric vehicle burns its fuel (mainly fossil fuels) off-board at the power generation plant.^[9] This methodology is used by carmakers to estimate credits into their overall Corporate Average Fuel Economy (CAFE) for manufacturing electric drive vehicles.^[8]

The equations for determining the petroleum equivalent fuel economy of electric vehicles are the following:^[9]

PEF = Eg * 1/0.15 * AF * DPF

where:

PEF = Petroleum-equivalent fuel economy

Eg = Gasoline-equivalent energy content of electricity factor

1/0.15 = "Fuel content" factor or incentive factor. DoE selected this value to keep consistency with existing regulatory and statutory procedures, and to provide a similar treatment to manufacturers of all types of alternative fuel vehicles

AF = Petroleum-fueled accessory factor

DPF = Driving pattern factor

The gasoline-equivalent energy content of electricity factor, abbreviated as Eg, is defined as:

Eg = gasoline-equivalent energy content of electricity = (Tg * Tt * C) / Tp

where:

Tg = U.S. average fossil-fuel electricity generation efficiency = 0.328

Tt = U.S. average electricity transmission efficiency = 0.924

Tp = Petroleum refining and distribution efficiency = 0.830

C = Watt-hours of energy per gallon of gasoline conversion factor = 33,705 Wh/gal

Eg = (0.328 * 0.924 * 33705)/0.830 = 12,307 Wh/gal

PEF = Eg * 1/0.15 * AF * DPF = 12,307 Wh/gal/0.15 * AF * DPF

PEF = 82,049 Wh/gal * AF * DPF

The petroleum-fueled accessory factor, AF, is equal to 1 if the electric drive vehicle does not have petroleum-powered accessories installed, and 0.90 if it does.

The driving pattern factor, DPF, is equal to 1, as DoE considered that electric vehicles eligible for inclusion in CAFE will offer capabilities, perhaps excepting driving range, similar to those of conventional vehicles.

In the example provided by the US DoE in its final rule, an electric car with an energy consumption of 265 Watt-hour per mile in urban driving, and 220 Watt-hour per mile in highway driving, resulted in a petroleum-equivalent fuel economy of 335.24 miles per gallon, based on a driving schedule factor of 55 percent urban, and 45 percent highway, and using a petroleum equivalency factor of 82,049 Watt-hours per gallon.^[9]

See also

• Alternative propulsion
• Corporate Average Fuel Economy (CAFE)
• Energy conversion efficiency
• Energy density
• Fuel efficiency in transportation
• Gasoline gallon equivalent (GGE)
• List of unusual units of measurement

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External links

• eGallon Calculator: Compare the costs of driving with electricity, U.S. Department of Energy
• Model Year 2014 Fuel Economy Guide , U.S. Environmental Protection Agency and U.S. Department of Energy, April 2014.