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Micro sign

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Title: Micro sign  
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Micro sign

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).[1] 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.


  • The size of the influenza virus is about .8 to 1.2 micrometers.[2]
Metric prefixes
Prefix Symbol 1000m 10n Decimal English word[n 1] Since[n 2]
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

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.[3]

Other abbreviating conventions

In some health care institutions, house rules deprecate the standard symbol for microgram, "µg", in prescribing or chart recording, because of the risk of misdose via the misreading of poor handwriting.[4] The two alternatives are to abbreviate as "mcg"[4] or to write out "microgram" in full (see also List of abbreviations used in medical prescriptions). But this deprecation, focused on bedside misdose avoidance in contexts where handwriting is often present, does not extend to all health care contexts and institutions (for example, some clinical laboratories' reports adhere to it whereas others don't[4]), and in physical sciences academia, "µg" remains the sole official abbreviation.


See also

hi:माइक्रो (उपसर्ग) he:תחיליות במערכת היחידות הבינלאומית#מיקרו nl:Micro simple:Micro-

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