Micro-

This article describes the SI prefix. For other meanings, 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 is 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 be represented using the letter u as in um for μm, or uF for μF. In some contexts, such as pharmacy, microgram is often written "mcg", which is nonstandard.

Metric prefixes

Prefix Symbol 1000m 10n Decimal Short scale Long scale Since yotta Y 10008 1024 1000000000000000000000000 Septillion Quadrillion 1991 zetta Z 10007 1021 1000000000000000000000 Sextillion Trilliard 1991 exa E 10006 1018 1000000000000000000 Quintillion Trillion 1975 peta P 10005 1015 1000000000000000 Quadrillion Billiard 1975 tera T 10004 1012 1000000000000 Trillion Billion 1960 giga G 10003 109 1000000000 Billion Milliard 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 Milliardth 1960 pico p 1000−4 10−12 0.000000000001 Trillionth Billionth 1960 femto f 1000−5 10−15 0.000000000000001 Quadrillionth Billiardth 1964 atto a 1000−6 10−18 0.000000000000000001 Quintillionth Trillionth 1964 zepto z 1000−7 10−21 0.000000000000000000001 Sextillionth Trilliardth 1991 yocto y 1000−8 10−24 0.000000000000000000000001 Septillionth Quadrillionth 1991

See also

• micrometre
• square micrometre
• microsecond