Micro-

This article is about the SI prefix. For other uses, see Micro (disambiguation).

Micro (µ) is a prefix in the metric system denoting a factor of 10^-6 (one millionth). Confirmed in 1960, the prefix comes from the Greek μικρός (mikrós), meaning "small".

The symbol for the prefix comes from the Greek letter μ (mu). It is the only SI prefix which uses a character not from the Latin alphabet.

Symbol encoding in character sets

For historical reasons, there are two different characters in Unicode, which appear slightly different in some fonts. The micro sign (µ) is encoded in the "Latin-1 Supplement" range identical to ISO/IEC 8859-1 (since 1985), at U+00B5 (Unicode 1.0, 1991). The Greek letter (μ) is encoded in the Greek range at U+03BC. In circumstances in which only the Latin alphabet is available, the prefix can (unofficially) be represented using the letter u as in um for µm, or uF for µF.

In pharmacy, nursing, and other health care fields, most especially in hospital environments, the standard symbol for microgram, "µg", is deprecated because of the risk of misdose via the misreading of poor handwriting. The two alternatives are to abbreviate as "mcg" or to write out "microgram" in full, the latter being best practice (see List of abbreviations used in medical prescriptions). In physical sciences academia, "µg" remains the sole official abbreviation.

Metric prefixes

Prefix Symbol 1000m 10n Decimal English word Since yotta Y  10008  1024 1000000000000000000000000 septillion 1991 zetta Z  10007  1021 1000000000000000000000 sextillion 1991 exa E  10006  1018 1000000000000000000 quintillion 1975 peta P  10005  1015 1000000000000000 quadrillion 1975 tera T  10004  1012 1000000000000 trillion 1960 giga G  10003  109 1000000000 billion 1960 mega M  10002  106 1000000 million 1960 kilo k  10001  103 1000 thousand 1795 hecto h  10002/3  102 100 hundred 1795 deca da  10001/3  101 10 ten 1795  10000  100 1 one – deci d  1000−1/3  10−1 0.1 tenth 1795 centi c  1000−2/3   10−2 0.01 hundredth 1795 milli m  1000−1  10−3 0.001 thousandth 1795 micro µ  1000−2  10−6 0.000001 millionth 1960 nano n  1000−3  10−9 0.000000001 billionth 1960 pico p  1000−4  10−12 0.000000000001 trillionth 1960 femto f  1000−5  10−15 0.000000000000001 quadrillionth 1964 atto a  1000−6  10−18 0.000000000000000001 quintillionth 1964 zepto z  1000−7  10−21 0.000000000000000000001 sextillionth 1991 yocto y  1000−8  10−24  0.000000000000000000000001 septillionth 1991

See also

• micrometre
• square micrometre
• microsecond