Micro (Greek letter μ, mu, non-italic) is a unit prefix in the metric system denoting a factor of 10−6 (one millionth).
U+00B5 µ MICRO SIGN (Alt+0181) is in the "Latin-1 Supplement" range identical to ISO/IEC 8859-1 (since 1987),[8] residing at this code point also in DEC MCS (since 1983) and ECMA-94 (since 1985).
Similarly, capacitor values according to the RKM code defined in IEC 60062 (since 1952) can be written as 4u7 (or 4U7) instead of 4μ7 if the Greek letter μ is not available.
In some health care institutions, house rules deprecate the standard symbol for microgram, "μg", in prescribing or chart recording, because of the risk of giving an incorrect dose because of the misreading of poor handwriting.
The alternative abbreviation may be ambiguous in rare circumstances in that mcg could also be read as a micrigram, i.e. 10−14 g; however the prefix micri is not standard, nor widely known, and is considered obsolete.