Billionth

One billionth is the reciprocal of a billion, which means it has one of two definitions depending on whether the long scale or short scale definition is being used.^[1]

Short scale

In the short (or American) scale, a billionth is equal to 0.000 000 001, or 1 x 10⁻⁹ in scientific notation. The prefix for this number is nano, and is abbreviated as "n" (for example, in electronics, one nanofarad would be written as 1 nF).^[2]

Long scale

In the long (or English) scale, a billionth is equal to 0.000 000 000 001, or 1 x 10⁻¹² in scientific notation. The prefix for this number is pico-, and is abbreviated as "p" (for example, in electronics, one picofarad would be written as 1 pF).^[3]

References

1. Gardner, J. W. (April 6, 1961), "How many is a billion?", Letters, New Scientist: 888.
2. Carstairs-McCarthy, Andrew (2002), An Introduction to English Morphology: Words and Their Structure, Edinburgh University Press, pp. 109–110, ISBN 9780748613267.
3. Bray, Charles (2001), Dictionary of Glass: Materials and Techniques, University of Pennsylvania Press, p. 243, ISBN 9780812236194.