Centimetre

Centimetre
a carpenters' ruler with centimetre divisions
Unit information
Unit system	SI and CGS
Unit of	length
Symbol	cm
Unit conversions
1 cm in ...	... is equal to ...
SI	10 mm
imperial & US system	~0.3937 in

A centimetre (international spelling as used by the International Bureau of Weights and Measures; symbol cm) or centimeter (American spelling) is a unit of length in the metric system, equal to one hundredth of a metre, centi being the SI prefix for a factor of ¹⁄₁₀₀.^[1] The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units.

Though for many physical quantities, SI prefixes for factors of 10³—like milli- and kilo-—are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements. A centimetre is approximately the width of the fingernail of an average adult person.

Equivalence to other units of length

1 centimetre	= 10 millimetres
	= 0.01 metres
	= 0.393700787401574803149606299212598425196850 inches
	(There are exactly 2.54 centimeters in one inch.)

One 1 millilitre is defined as one cubic centimetre, under the SI system of units.

Other uses

In addition to its use in the measurement of length, the centimetre is used:

• sometimes, to report the level of rainfall as measured by a rain gauge ^[2]
• in the CGS system, the centimetre is used to measure capacitance, where 1 cm of capacitance = 1.113×10⁻¹² farads^[3]
• in maps, centimetres are used to make conversions from map scale to real world scale (kilometres)
• to represent second moment of areas (cm⁴)
• as the inverse of the kayser, a CGS unit, and thus a non-SI metric unit of wavenumber: 1 kayser = 1 wave per centimetre; or, more generally, (wavenumber in kaysers) = 1/(wavelength in centimetres). The SI unit of wavenumber is the inverse metre, m⁻¹.

Unicode symbols

For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:^[4]

• centimetre (㎝) – code 339D
• square centimetre (㎠) – code 33A0
• cubic centimetre (㎤) – code 33A4

They are mostly used only with East Asian fixed-width CJK fonts, because they are equal in size to one Chinese character.

See also

• 1 E-2 m
• Conversion of units, for comparison with other units of length
• Reciprocal centimetre
• Orders of magnitude (length)

References

1. "Decimal multiples and submultiples of SI units". Bureau International des Poids et Mesures. 2014. Retrieved 5 July 2015.
2. Rain Measurement, Rain Gauge, Wireless Rain Gauge, Rain Gage, Rain Gauge Data
3. Capacitance - from Eric Weisstein's World of Physics
4. CJK Compatibility excerpt from The Unicode Standard, Version 4.1.

• CJK Compatibility excerpt from The Unicode Standard, Version 4.4 and co-exterior users.