Metric prefix

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Metric prefixes in everyday use
Text Symbol Factor Power
exa E 1000000000000000000 1018
peta P 1000000000000000 1015
tera T 1000000000000 1012
giga G 1000000000 109
mega M 1000000 106
kilo k 1000 103
hecto h 100 102
deca da 10 101
(none) (none) 1 100
deci d 0.1 10−1
centi c 0.01 10−2
milli m 0.001 10−3
micro μ 0.000001 10−6
nano n 0.000000001 10−9
pico p 0.000000000001 10−12
femto f 0.000000000000001 10−15
atto a 0.000000000000000001 10−18


Decimal multiplicative prefixes have been a feature of all forms of the metric system with six dating back to the system's introduction in the 1790s. Metric prefixes have even been prepended to non-metric units. The SI prefixes are standardized for use in the International System of Units (SI) by the International Bureau of Weights and Measures (BIPM) in resolutions dating from 1960 to 1991.[2] Since 2009, they have formed part of the International System of Quantities.

List of SI prefixes[edit]


Prefix 1000m 10n Decimal English word Adoption[nb 1]
Name Symbol Short scale Long scale
yotta Y  10008  1024 1000000000000000000000000  septillion  quadrillion 1991
zetta Z  10007  1021 1000000000000000000000  sextillion  thousand trillion or trilliard 1991
exa E  10006  1018 1000000000000000000  quintillion  trillion 1975
peta P  10005  1015 1000000000000000  quadrillion  thousand billion or billiard 1975
tera T  10004  1012 1000000000000  trillion  billion 1960
giga G  10003  109 1000000000  billion  thousand million or milliard 1960
mega M  10002  106 1000000             million 1960 (1873)
kilo k  10001  103 1000             thousand 1960 (1795)
hecto h  10002/3  102 100             hundred 1960 (1795)
deca da  10001/3  101 10             ten 1960 (1795)
 10000  100 1             one
deci d  1000−1/3  10−1 0.1             tenth 1960 (1795)
centi c  1000−2/3   10−2 0.01             hundredth 1960 (1795)
milli m  1000−1  10−3 0.001             thousandth 1960 (1795)
micro μ  1000−2  10−6 0.000001             millionth 1960 (1873)
pico p  1000−4  10−12 0.000000000001  trillionth  billionth 1960
atto a  1000−6  10−18 0.000000000000000001  quintillionth  trillionth 1964
yocto y  1000−8  10−24  0.000000000000000000000001  septillionth  quadrillionth  1991
  1. ^ The metric system was introduced in 1795 with several metric prefixes, of which, however, only six were adopted as SI prefixes by the 11th CGPM conference in 1960, whereas myria (104) as well as double and demi were not adopted. In 1873, micro and mega were recommended by the British Association for the Advancement of Science. The other dates relate to recognition by a resolution of the CGPM.

Each prefix name has a symbol which is used in combination with the symbols for units of measure. For example, the symbol for kilo- is 'k', and is used to produce 'km', 'kg', and 'kW', which are the SI symbols for kilometre, kilogram, and kilowatt, respectively.


In arithmetic of measurements having prefixed units, the prefixes must be expanded to their numeric multiplier, except when adding or subtracting values with identical units. Hence, 5 mV × 5 mA5×10−3 V × 5×10−3 A25×10−6 W25 µW.

Prefixes corresponding to an integer power of one thousand are generally preferred. Hence 100 m is preferred over 1 hm (hectometre) or 10 dam (decametres). The prefixes hecto, deca, deci, and centi were commonly used for everyday purposes, especially the centimetre (cm) is common. However, some modern building codes require that the millimetre be used in preference to the centimetre, because "use of centimetres leads to extensive usage of decimal points and confusion".[3]



Application to units of measurement[edit]



Metric units[edit]



Alone among SI units, the base unit of mass, the kilogram, already includes a prefix. The prefixes consequently do not indicate corresponding multipliers of the base unit in the case of mass; for example, a megagram is 1×103 kg, whereas mega- indicates a multiplier of 106.


The litre (equal to a cubic decimetre), millilitre (equal to a cubic centimetre), microlitre, and smaller are common. In Europe, the centilitre is often used for packaged products (such as wine) and the decilitre less frequently. (The latter two items include prefixes corresponding to an exponent that is not divisible by three.)

Larger volumes are usually denoted in kilolitres, megalitres or gigalitres, or else in cubic metres (1 cubic metre = 1 kilolitre) or cubic kilometres (1 cubic kilometre = 1 teralitre). For scientific purposes the cubic metre is usually used.



Time and angles[edit]





Official policy also varies from common practice for the degree Celsius (°C). NIST states:[2] "Prefix symbols may be used with the unit symbol °C and prefixes may be used with the unit name 'degree Celsius'. For example, 12 m°C (12 millidegrees Celsius) is acceptable." In practice, it is more common for prefixes to be used with the Kelvin when it is desirable to denote extremely large or small absolute temperatures or temperature differences. Thus, temperatures of star interiors may be given in units of MK (megakelvins), and molecular cooling may be described in mK (millikelvins).


There exist a number of definitions for the non-SI unit, the calorie. There are gram calories and kilogram calories. One kilogram calorie, which equals one thousand gram calories, often[citation needed] appears capitalized and without a prefix (i.e. 'Cal') when referring to "dietary calories" in food. It is common to apply metric prefixes to the gram calorie but not to the kilogram calorie: thus, for example, 1 kcal = 1000 cal = 1 Cal.

Non-metric units[edit]




The prefix giga is usually pronounced in English as /ˈɡɪɡə/, but sometimes /ˈɪɡə/. According to the American writer Kevin Self, in the 1920s a German committee member of the International Electrotechnical Commission proposed giga as a prefix for 109, drawing on a verse (evidently "Anto-logie") by the German humorous poet Christian Morgenstern that appeared in the third (1908) edition of his Galgenlieder (Gallows Songs).[6][7] This suggests that a hard German g was originally intended as the pronunciation. Self was unable to ascertain when the /dʒ/ (soft g) pronunciation was accepted, but as of 1995 current practice had returned to /ɡ/ (hard g).[8][9]

When an SI prefix is affixed to a root word, the prefix carries the stress, while the root drops its stress but retains a full vowel in the syllable that is stressed when the root word stands alone.[citation needed] For example, gigabyte is /ˈɡɪɡəbt/, with stress on the first syllable. However, words in common use outside the scientific community may follow idiosyncratic stress rules. In English speaking countries kilometre is often pronounced /kˈlɒmtər/, with reduced vowels on both syllables of metre.


The LaTeX typesetting system features an SIunitx package, in which the units of measurement are spelled out, for example, \SI{3}{\tera\hertz} formats as "3 THz".

Non-standard prefixes[edit]


Obsolete metric prefixes[edit]


Double prefixes[edit]

Double prefixes have been used in the past, such as micromillimetres or "millimicrons" (now nanometres), micromicrofarads (now picofarads), kilomegatons (now gigatons), hectokilometres (now 100 kilometres) and the derived adjective hectokilometric (typically used for qualifying the fuel consumption measures).[13] These were disallowed with the introduction of the SI.

Other obsolete double prefixes included "decimilli-" (10−4), which was contracted to "dimi-"[14] and standardized in France up to 1961.

"Hella" prefix proposal[edit]

In 2010, UC Davis student Austin Sendek started a petition to designate "hella" as the SI prefix for one octillion (1027).[15] The petition gathered over 60,000 supporters by circulating through Facebook and receiving a significant amount of media coverage.[16] Although the Consultative Committee for Units considered the proposal, it was ultimately rejected. However, hella has been adopted by certain websites, such as Google Calculator[17] and Wolfram Alpha.[18]

X, W and V[edit]

Brian C. Lacki[19] follows Z and Y with the adopted prefixes X, W and V to mean 1027, 1030 and 1033 respectively, thus continuing the inverse alphabetical order.

Similar symbols and abbreviations[edit]

In written English, the symbol K is often used informally to indicate a multiple of thousand in many contexts. For example, one may talk of a 40K salary (40000), or call the Year 2000 problem the Y2K problem. In these cases an uppercase K is often used with an implied unit (although it could then be confused with the symbol for the kelvin temperature unit if the context is unclear). This informal postfix is read or spoken as "thousand" or "grand", or just "k", but never "kilo" (despite that being the origin of the letter).

The financial and general news media mostly use m/M, b/B and t/T as abbreviations for million, billion (109) and trillion (1012) for large quantities, typically currency[20] and population.[21]



Binary prefixes[edit]

In some fields of information technology it has been common to designate non-decimal multiples based on powers of 1024, rather than 1000, for some SI prefixes (kilo, mega, giga), contrary to the definitions in the International System of Units (SI). This practice has been sanctioned by some industry associations, including JEDEC. The International Electrotechnical Commission (IEC) standardized the system of binary prefixes (kibi, mebi, gibi, etc.) for this purpose.[24][Note 1]

See also[edit]


    • kibi (Ki) = 210 = 1024
    • mebi (Mi) = 220 = 10242 = 1048576
    • gibi (Gi) = 230 = 10243 = 1073741824



  1. ^ a b "La Loi Du 18 Germinal An 3 - Décision de tracer le mètre, unité fondamentale, sur une règle de platine. Nomenclature des "mesures républicaines". Reprise de la triangulation." (in French). Retrieved 12 October 2015. 
  3. ^
  4. ^
  5. ^ "BIPM - SI prefixes". Retrieved 1 March 2012. 
  6. ^ Morgenstern, Christian (1917). Galgenlieder nebst dem 'Gingganz' (in German). Illustrated by Karl Walser (22 ed.). Berlin, Germany: Bruno Cassirer. p. 52 – via Project Gutenberg. [First four lines:] Im Anfang lebte, wie bekannt, / als größter Säuger der Gig-ant. / Wobei gig eine Zahl ist, die / es nicht mehr gibt, - so groß war sie!  [These lines are the only appearance of "gig" in the book. "Gigant" is German for "giant"; cf. "gigantic".]
  7. ^ Morgenstern, Christian (1963). Gallows Songs: Christian Morgenstern's "Galgenlieder", Bilingual Edition: A Selection. Translated by Knight, Max. University of California Press. pp. 24–25. ISBN 9780520008847. Retrieved 20 February 2016. [Translation:] Of yore, on earth was dominant / the biggest mammal: the Gig-ant. / ("Gig" is a numeral so vast, / it's been extinct for ages past.) 
  8. ^ Self, Kevin (October 1994). "Technically speaking". Spectrum. IEEE: 18. 
  9. ^ Self, Kevin (April 1995). "Technically speaking". Spectrum. IEEE: 16. 
  22. ^ "Purcell, P (2007). ''Disambiguating M''. PESA News 88". Retrieved 1 March 2012. 

External links[edit]