This article describes the SI prefix. For other meanings, see
Micro.
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 |
| 10002⁄3 | 102 | hecto | h | 1795 | Hundred | 100 |
| 10001⁄3 | 101 | deca | da | 1795 | Ten | 10 |
| 10000 | 100 | (none) | (none) | NA | One | 1 |
| 1000−1⁄3 | 10−1 | deci | d | 1795 | Tenth | 0.1 |
| 1000−2⁄3 | 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 |
- The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.
- The 1948 recognition of the micron by the CGPM was abrogated in 1967.
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[edit] References
- ^ International Bureau of Weights and Measures (2006), The International System of Units (SI) (8th ed.), ISBN 92-822-2213-6, http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf
- ^ ISO 2955, Table 2.
[edit] See also
