A decimal submultiplier prefix in SI, signifying one millionth of the unit to which it is attached. Symbol, “µ”.  The prefix and its symbol were adopted by resolution 12 of the 11th Conférence Générale des Poids et Mesures in 1960.¹

Several other symbols have been used for micro-. In lists of vitamin pill contents, “microgram” is often abbreviated “mcg”. In copy produced on a typewriter, µ was often represented by the letter “u.” Prefixed to farad, it was often abbreviated as “m,” as in “mmf,” for micromicrofarad.

In Chinese, the micro- is wei.

1. Comptes rendus des séances de la 11é conference generale des poids et mesures.
Paris: Gauthier-Villars, 1960.

Page 87.


Barry N. Taylor and Ambler Thompson, editors.
The International System of Units (SI) pdf logo
NIST Special Publication 330, 2008 Edition.

“United States version of the English text of the eighth edition (2006) of the International Bureau of Weights and Measures publication Le Système International d’ Unités (SI)” This publication is the definitive guide for the United States, but the ultimate authority is the original, French version. For the symbols for the prefixes, see page 29.

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