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From Wikipedia, the free encyclopedia

The term micro (µ) is a prefix in the SI and other systems of units denoting a factor of 10−6 (one millionth).[1] Confirmed in 1960, the prefix comes from the Greek μικρός (mikrós), meaning "small".

The symbol for it is the micro sign µ, the Greek letter mu (μ). For historical reasons, these are two different characters in Unicode, which appear slightly different in some fonts. The micro sign 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 is encoded in the Greek range at U+03BC.

In circumstances where only the Latin alphabet is available, the prefix can be represented using the letter u as in "um" for µm, or "uF" for µF.[2] In some contexts, such as pharmacy, microgram is often written mcg, which is nonstandard.

SI prefixes
1000m 10n Prefix Symbol Since[1] Short scale Long scale Decimal
10008 1024 yotta Y 1991 Septillion Quadrillion 1000000000000000000000000
10007 1021 zetta Z 1991 Sextillion Trilliard 1000000000000000000000
10006 1018 exa E 1975 Quintillion Trillion 1000000000000000000
10005 1015 peta P 1975 Quadrillion Billiard 1000000000000000
10004 1012 tera T 1960 Trillion Billion 1000000000000
10003 109 giga G 1960 Billion Milliard 1000000000
10002 106 mega M 1960 Million 1000000
10001 103 kilo k 1795 Thousand 1000
100023 102 hecto h 1795 Hundred 100
100013 101 deca da 1795 Ten 10
10000 100 (none) (none) NA One 1
100013 10−1 deci d 1795 Tenth 0.1
100023 10−2 centi c 1795 Hundredth 0.01
1000−1 10−3 milli m 1795 Thousandth 0.001
1000−2 10−6 micro µ 1960[2] Millionth 0.000001
1000−3 10−9 nano n 1960 Billionth Milliardth 0.000000001
1000−4 10−12 pico p 1960 Trillionth Billionth 0.000000000001
1000−5 10−15 femto f 1964 Quadrillionth Billiardth 0.000000000000001
1000−6 10−18 atto a 1964 Quintillionth Trillionth 0.000000000000000001
1000−7 10−21 zepto z 1991 Sextillionth Trilliardth 0.000000000000000000001
1000−8 10−24 yocto y 1991 Septillionth Quadrillionth 0.000000000000000000000001
  1. The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.
  2. The 1948 recognition of the micron by the CGPM was abrogated in 1967.


  1. ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), ISBN 92-822-2213-6,  
  2. ^ ISO 2955, Table 2.

See also



Up to date as of January 15, 2010
(Redirected to micro- article)

Definition from Wiktionary, a free dictionary

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See also micro




From Ancient Greek μικρός (mikros), small).



SI prefix
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  1. Very small.
  2. (metric units) One millionth.

Usage notes

  • (one millionth): Officially, micro- is abbreviated as µ- (the Greek letter mu); for example, one second is 1s, so one microsecond is 1µs. However, for many purposes this is inconvenient, so writers often use either u- (for its similar appearance to µ-) or mc-, producing, for example, 1um (one micrometer) and 1mcg (one microgram).


Derived terms

Look at pages starting with micro.


The translations below need to be checked and inserted above into the appropriate translation tables, removing any numbers. Numbers do not necessarily match those in definitions. See instructions at Help:How to check translations.




  1. micro- (very small)
  2. micro- (SI prefix)




  1. micro- (very small)
  2. micro- (SI prefix)

Derived terms

See Category:Italian words prefixed with micro-


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