Micro-

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This article describes the SI prefix. For other meanings, see Micro.
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micro- 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 is sometimes represented using the letter u as in "um" for µm, or "uV" for µV. In some contexts, such as pharmacy, micrograms are often written mcg. Neither variant is standard.

SI prefixes
1000n 10n Prefix Symbol Short scale Long scale Decimal equivalent in SI writing style
10008 1024 yotta- Y Septillion Quadrillion 1 000 000 000 000 000 000 000 000
10007 1021 zetta- Z Sextillion Trilliard (thousand trillion) 1 000 000 000 000 000 000 000
10006 1018 exa- E Quintillion Trillion 1 000 000 000 000 000 000
10005 1015 peta- P Quadrillion Billiard (thousand billion) 1 000 000 000 000 000
10004 1012 tera- T Trillion Billion 1 000 000 000 000
10003 109 giga- G Billion Milliard (thousand million) 1 000 000 000
10002 106 mega- M Million 1 000 000
10001 103 kilo- k Thousand 1 000
10002/3 102 hecto- h Hundred 100
10001/3 101 deca- da Ten 10
10000 100 (none) (none) One 1
1000−1/3 10−1 deci- d Tenth 0.1
1000−2/3 10−2 centi- c Hundredth 0.01
1000−1 10−3 milli- m Thousandth 0.001
1000−2 10−6 micro- µ Millionth 0.000 001
1000−3 10−9 nano- n Billionth Milliardth 0.000 000 001
1000−4 10−12 pico- p Trillionth Billionth 0.000 000 000 001
1000−5 10−15 femto- f Quadrillionth Billiardth 0.000 000 000 000 001
1000−6 10−18 atto- a Quintillionth Trillionth 0.000 000 000 000 000 001
1000−7 10−21 zepto- z Sextillionth Trilliardth 0.000 000 000 000 000 000 001
1000−8 10−24 yocto- y Septillionth Quadrillionth 0.000 000 000 000 000 000 000 001