A metric prefix is a unit of measurement prefix that precedes a basic whole of measure to indicate a multiple or submultiple of the unit. All metric prefixes used today are decadic. Each prefix has a unique symbol that is prepended to any unit symbol. The prefix kilo, for example, may be added to gram to indicate multiplication by one thousand : one kilogram is equal to one thousand gram. The prefix milli, besides, may be added to metre to indicate division by one thousand ; one millimeter is equal to one onethousandth of a meter. Decimal multiplicative prefixes have been a feature of all forms of the metric function system, with six of these dating bet on to the organization ‘s introduction in the 1790s. Metric prefixes have besides been used with some nonmetric units. The SI prefixes are measured prefixes that were standardized for habit in the International System of Units ( SI ) by the International Bureau of Weights and Measures ( BIPM ) in resolutions dating from 1960 to 1991. [ 1 ] Since 2009, they have formed part of the International System of Quantities. They are besides used in the Unified Code for Units of Measure ( UCUM )
number of SI prefixes [edit ]
The BIPM specifies twenty prefixes for the International System of Units ( SI ).
Reading: Metric prefix
Each prefix name has a symbol that is used in combination with the symbols for units of measure. For example, the symbol for kilo is k, and is used to produce kilometer, kilogram, and kilowatt, which are the SI symbols for kilometer, kilogram, and kilowatt, respectively. Except for the early prefixes of kilo, hecto, and deca, the symbols for the multiplicative prefixes are uppercase letters, and those for the fractional prefixes are lowercase letters. [ 2 ] There is a Unicode symbol for micro µ for use if the greek letter μ is unavailable. [ note 1 ] When both are unavailable, the visually similar lowercase Latin letter u is normally used alternatively. SI unit symbols are never italicised. Prefixes corresponding to an integer exponent of one thousand are by and large preferred. Hence 100 m is preferred over 1 hm ( hectometer ) or 10 decameter ( decametres ). The prefix deci, and centi, and less frequently hecto and deca, are normally used for everyday purposes, and the centimeter ( centimeter ) is specially coarse. Some modern build codes require that the millimeter be used in preference to the centimeter, because “ use of centimetres leads to extensive custom of decimal points and confusion ”. [ 3 ] Prefixes may not be used in combination. This besides applies to mass, for which the SI base unit ( kilogram ) already contains a prefix. For example, milligram ( magnesium ) is used rather of microkilogram ( μkg ). In the arithmetic of measurements having units, the units are treated as multiplicative factors to values. If they have prefixes, all but one of the prefixes must be expanded to their numeric multiplier, except when combining values with identical units. hence :

5 mendelevium ×
5 ma =
5
×
10−3 V ×
5
×
10−3 adenine =
25
×
10−6 V⋅A =
25 μW.

5.00 millivolt +
10 μV =
5.00 millivolt +
0.01 millivolt =
5.01 mendelevium.
When powers of units occur, for example, squared or cubed, the multiplicative prefix must be considered separate of the unit, and therefore included in the exponentiation :
 1 km2 means one square kilometre, or the area of a square of
1000 molarity by
1000 megabyte and not
1000 square metres.
 2 Mm3 means two cubic megametres, or the volume of two cubes of
1
000
000
thousand by
1
000
000
molarity by
1
000
000
thousand or
2
×
1018 m3, and not
2
000
000
cubic metres (
2
×
106 m3).
 Examples

5 centimeter =
5
×
10−2 thousand = 5 × 0.01 m = 0.05 m.

9 km2 = 9 × ( 103 thousand ) 2 = 9 × ( 103 ) 2 × m2 =
9
×
106 m2 = 9 ×
1
000
000
m2
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=
9
000
000
m2.
 3 MW =
3
×
106 W = 3 ×
1
000
000
W =
3
000
000
W.
application to units of measurement [edit ]
The use of prefixes can be traced back to the presentation of the system of measurement system in the 1790s, long before the 1960 introduction of the SI. The prefixes, including those introduced after 1960, are used with any metric unit whole, whether formally included in the SI or not ( e.g., millidynes and milligauss ). Metric prefix may besides be used with nonmetric units. The choice of prefixes with a given unit of measurement is normally dictated by convenience of use. Unit prefixes for amounts that are much larger or smaller than those actually encountered are rarely used .
Metric units [edit ]
batch [edit ]
The units kilogram, gram, milligram, microgram, and smaller are normally used for measurement of mass. however, megagram, gigagram, and larger are rarely used ; tonnes ( and kilotonnes, megatonnes, etc. ) or scientific note are used rather. Megagram and teragram are occasionally used to disambiguate the metric unit metric ton from other units with the diagnose “ short ton ”. [ citation needed ] The kilogram is the only base unit of the International System of Units that includes a system of measurement prefix .
book [edit ]
The liter ( equal to a cubic decimeter ), millilitre ( equal to a cubic centimeter ), microlitre, and smaller are coarse. In Europe, the centiliter is much used for liquids, and the deciliter is used less frequently. Bulk agrarian products, such as grain, beer and wine, are often measured in hectolitres ( each 100 litres in size ). Larger volumes are normally denoted in kilolitres, megalitres or gigalitres, or else in cubic metres ( 1 cubic meter = 1 kiloliter ) or cubic kilometres ( 1 cubic kilometer = 1 teralitre ). For scientific purposes, the cubic meter is normally used .
length [edit ]
The kilometer, meter, centimeter, millimeter, and smaller units are common. The decimeter is rarely used. The micrometre is often referred to by the older nonSI name micron. In some fields, such as chemistry, the ångström ( 0.1 new mexico ) has been used normally alternatively of the nanometer. The femtometer, used chiefly in particle physics, is sometimes called a femtometer. For large scales, megametre, gigametre, and larger are rarely used. alternatively, ad hoc nonmetric units are used, such as the solar radius, astronomic units, unhorse years, and parsec ; the astronomic unit is mentioned in the SI standards as an bear nonSI unit of measurement .
time [edit ]
Prefixes for the SI standard unit second are most normally encountered for quantities less than one moment. For larger quantities, the system of minutes ( 60 seconds ), hours ( 60 minutes ) and days ( 24 hours ) is accepted for consumption with the SI and more normally used. When address of spans of time, the distance of the day is normally standardized to 86400 seconds indeed as not to create issues with the irregular jump moment. Larger multiples of the second such as kiloseconds and megaseconds are occasionally encountered in scientific context, but are rarely used in common parlance. For longscale scientific work, particularly in astronomy, the julian year or annum is a exchangeable form of the year, equal to precisely 31557600 SI seconds ( 365 days, 6 hours ). The whole is then named because it was the average length of a year in the julian calendar. long time periods are then expressed by using metric unit prefixes with the annum, such as megaannum or gigaannum .
angle [edit ]
The SI unit of angle is the radian, but degrees, minutes, and seconds see some scientific use .
temperature [edit ]
official policy besides varies from common exercise for the degree Celsius ( °C ). national institute of standards and technology states : [ 4 ] “ Prefix symbols may be used with the unit of measurement symbol °C and prefix names may be used with the unit name degree Celsius. For example, 12 m°C ( 12 millidegrees Celsius ) is satisfactory. ” In practice, it is more common for prefixes to be used with the kelvin when it is desirable to denote highly large or modest absolute temperatures or temperature differences. frankincense, temperatures of star interiors may be given in units of MK ( megakelvins ), and molecular cool may be described in mK ( millikelvins ) .
Energy [edit ]
In manipulation the joule and kilojoule are common, with larger multiples seen in restrict context. In addition, the kilowatt hour, a composite unit formed from the kilowatt and hour, is often used for electric energy ; other multiples can be formed by modifying the prefix of watt ( e.g. terawatt hour ). There exist a number of definitions for the nonSI unit of measurement, the calorie. There are gram calories and kilogram calories. One kilogram calorie, which equals one thousand gram calories, much appears capitalize and without a prefix ( i.e. Cal ) when referring to “ dietary calories “ in food. [ 5 ] It is common to apply metric function prefixes to the gram calorie, but not to the kilogram calorie : therefore, 1 kcal = 1000 cal = 1 Cal .
nonmetric units [edit ]
Metric prefixes are wide used outside the system of measurement SI system. coarse examples include the megabyte and the decibel. Metric prefixes rarely appear with imperial or uracil units except in some special cases ( for example, microinch, kilofoot, kilopound ). They are besides used with other speciate units used in particular fields ( for example, megaelectronvolt, gigaparsec, millibarn ). They are besides occasionally used with currentness units ( for example, gigadollar ), chiefly by people who are familiar with the prefixes from scientific use. [ citation needed ] In astronomy, geology, and paleontology, the class, with symbol a ( from the Latin annus ), is normally used with metric unit prefixes : ka, Ma, and Ga. official policies about the use of SI prefixes with nonSI units vary slightly between the International Bureau of Weights and Measures ( BIPM ) and the american National Institute of Standards and Technology ( NIST ). For case, the NIST advises that ‘to debar confusion, prefix symbols ( and prefix names ) are not used with the timerelated unit symbols ( names ) min ( minute ), h ( hour ), five hundred ( day ) ; nor with the anglerelated symbols ( names ) ° ( degree ), ′ ( minute ), and ″ ( moment ), [ 4 ] whereas the BIPM adds information about the use of prefixes with the symbol as for second when they state : “ however astronomers use milliarcsecond, which they denote mas, and microarcsecond, μas, which they use as units for measuring very little angles. ” [ 6 ] An advantage of the SI arrangement decimal fraction prefixes is that they make for chasteness of calculation and conversion involving units of different sizes ; consider for case the ease of buying 13 items of 390 g weight at €12.34 per kilogram, compared with items of 13+3⁄4 oz at $ 4.79 per egyptian pound ( or, worse, with old nonmetric currency : £4/15/9½ ). In the units used in the US, compound of units that are not decimal multiples of each other is much avoided by not mixing the units used, e.g., using inches, feet or miles only : 89 inches rather than 7 feet 5 inches ( or 2 yards, 1 infantry 5 inches ) .
presentation [edit ]
pronunciation [edit ]
When a metric prefix is affixed to a beginning word, the prefix carries the stress, while the settle drops its stress but retains a full vowel in the syllable that is stressed when the root discussion stands alone. [ citation needed ] For example, kilobyte is, with stress on the first syllable. however, units in coarse use outside the scientific community may be stressed idiosyncratically. In englishspeaking countries, kilometre is the most conspicuous example. It is often pronounced, with reduce vowels on both syllables of metre. This stress is not applied to early multiples or submultiples of meter, or to early units prefixed with kilo. The prefix giga is normally pronounced in English as, with hard ⟨g⟩ as in get, but sometimes, with indulgent ⟨g⟩ as in gin. [ 7 ] [ citation needed ]
Typesetting [edit ]
The LaTeX typeset system features an SIunitx software in which the units of measurement are spelled out, for exercise, \SI{3}{\tera\hertz}
formats as “ 3 THz ” .
Nonstandard prefixes [edit ]
Distance marker on the Rhine : 36 ( XXXVI ) myriametres from Basel. The state distance is 360 kilometer ; the decimal mark in Germany is a comma .
Obsolete metric function prefixes [edit ]
Some of the prefixes once used in the metric function system have fallen into neglect and were not adopted into the SI. [ 8 ] [ 9 ] [ 10 ] The decimal fraction prefix for ten thousand, myria ( sometimes besides written as myrio ), and the binary prefixes double ( 2× ) and demi ( 1/2× ) were parts of the original metric function system adopted by France in 1795, [ 11 ] but were not retained when the SI prefixes were internationally adopted by the 11th CGPM conference in 1960. other metric unit prefixes used historically include hebdo ( 107 ) and micri ( 10−14 ) .
Double prefixes [edit ]
double prefixes have been used in the past, such as micromillimetres or millimicrons ( now nanometres ), micromicrofarads ( μμF ; immediately picofarads, pF ), kilomegatons ( now gigatons ), hectokilometres ( immediately 100 kilometres ) and the deduce adjectival hectokilometric ( typically used for qualifying the fuel pulmonary tuberculosis measures ). [ 12 ] These are not compatible with the SI. other disused double prefixes included “ decimilli ” ( 10−4 ), which was contracted to “ dimi ” [ 13 ] and standardized in France improving to 1961 .
exchangeable symbols and abbreviations [edit ]
In written English, the symbol K is often used informally to indicate a multiple of thousand in many contexts. For case, one may talk of a 40K salary ( 40000 ), or call the year 2000 problem the Y2K problem. In these cases, an capital K is much used with an imply unit ( although it could then be confused with the symbol for the kelvin temperature unit if the context is illdefined ). This informal suffix is read or spoken as “ thousand ” or “ thousand ”, or merely “ kilobyte ”. The fiscal and general news program media by and large use megabyte or M, bacillus or B, and t or T as abbreviations for million, billion ( 109 ) and trillion ( 1012 ), respectively, for large quantities, typically currency [ 14 ] and population. [ 15 ] The medical and automotive fields in the United States use the abbreviations cc or ccm for cubic centimetres. 1 cubic centimeter is equivalent to 1 millilitre. For closely a hundred, engineers used the abbreviation MCM to designate a “ thousand circular mils “ in specifying the crosssection area of big electrical cables. Since the mid1990s, kcmil has been adopted as the official appellation of a thousand circular mils, but the designation MCM still remains in wide use. A similar system is used in natural flatulence sales in the United States : m ( or M ) for thousands and mm ( or MM ) for millions of british thermal units or therms, and in the oil industry, [ 16 ] where MMbbl is the symbol for “ millions of barrels ”. This use of the capital letter M for “ thousand ” is from Roman numerals, in which M means 1000. [ 17 ]
Binary prefixes [edit ]
In some fields of information engineering, it has been common to designate nondecimal multiples based on powers of 1024, preferably than 1000, for some SI prefixes ( kilo, mega, giga ), contrary to the definitions in the International System of Units ( SI ). This rehearse was once 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. [ 18 ] [ Note 2 ]
See besides [edit ]
Notes [edit ]
 ^ On Microsoft Windows systems, Alt+230 will yield the symbol for micro µ. With macOS systems it is ⌥ Opt+Y or ⌥ Opt+m, and with Linux systems it is Ctrl+⇧ Shift+u b5space .
 ^
 kibi (Ki) = 210 =
1024,
 mebi (Mi) = 220 =
10242 =
1
048
576
,
 gibi (Gi) = 230 =
10243 =
1
073
741
824
,
etc. The names and symbols of the binary prefixes proposed by the IEC includeetc .
 kibi (Ki) = 210 =
References [edit ]
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