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46-578: Deci- (symbol d ) is a decimal unit prefix in the metric system denoting a factor of one tenth. Proposed in 1793, and adopted in 1795, the prefix comes from the Latin decimus , meaning "tenth". Since 1960, the prefix is part of the International System of Units (SI). A frequent use of the prefix is in the unit deciliter (dl), common in food recipes; many European homes have a deciliter measure for flour, water, etc. A common measure in engineering

92-602: A revision in November 2018 that defines the kilogram by defining the Planck constant to be exactly 6.626 070 15 × 10  kg⋅m ⋅s , effectively defining the kilogram in terms of the second and the metre. The new definition took effect on 20 May 2019. Prior to the redefinition, the kilogram and several other SI units based on the kilogram were defined by a man-made metal artifact: the Kilogramme des Archives from 1799 to 1889, and

138-408: A " μ " key, so it is necessary to use a key-code; this varies depending on the operating system, physical keyboard layout, and user's language. The LaTeX typesetting system features an SIunitx package in which the units of measurement are spelled out, for example, \qty{3}{\tera\hertz} formats as "3 THz". The use of prefixes can be traced back to the introduction of the metric system in

184-607: A cylinder composed of platinum–iridium , the International Prototype of the Kilogram (IPK), became the standard of the unit of mass for the metric system and remained so for 130 years, before the current standard was adopted in 2019 . The kilogram is defined in terms of three defining constants: The formal definition according to the General Conference on Weights and Measures (CGPM) is: The kilogram, symbol kg,

230-578: A driver, in order to maintain symmetry. The prefixes from tera- to quetta- are based on the Ancient Greek or Ancient Latin numbers from 4 to 10, referring to the 4th through 10th powers of 10 . The initial letter h has been removed from some of these stems and the initial letters z , y , r , and q have been added, ascending in reverse alphabetical order, to avoid confusion with other metric prefixes. When mega and micro were adopted in 1873, there were then three prefixes starting with "m", so it

276-481: A mass measurement instrument such as a Kibble balance as a primary standard for the kilogram mass. The kilogram was originally defined in 1795 during the French Revolution as the mass of one litre of water . The current definition of a kilogram agrees with this original definition to within 30 parts per million . In 1799, the platinum Kilogramme des Archives replaced it as the standard of mass. In 1889,

322-460: 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 appears capitalised 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, 1 kcal = 1000 cal = 1 Cal. Metric prefixes are widely used outside

368-479: A reintroduction of compound prefixes (e.g. kiloquetta- for 10 ) if a driver for prefixes at such scales ever materialises, with a restriction that the last prefix must always be quetta- or quecto- . This usage has not been approved by the BIPM. 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 ( 40 000 ), or call

414-447: A weight measurement to a mass and therefore require precise measurement of the strength of gravity in laboratories ( gravimetry ). All approaches would have precisely fixed one or more constants of nature at a defined value. Because an SI unit may not have multiple prefixes (see SI prefix ), prefixes are added to gram , rather than the base unit kilogram , which already has a prefix as part of its name. For instance, one-millionth of

460-541: A written specification. At the 94th Meeting of the CIPM in 2005, it was recommended that the same be done with the kilogram. In October 2010, the CIPM voted to submit a resolution for consideration at the General Conference on Weights and Measures (CGPM), to "take note of an intention" that the kilogram be defined in terms of the Planck constant , h (which has dimensions of energy times time, thus mass × length / time) together with other physical constants. This resolution

506-635: Is described as "a common informal name" on Russ Rowlett's Dictionary of Units of Measurement. When the United States Congress gave the metric system legal status in 1866, it permitted the use of the word kilo as an alternative to the word kilogram , but in 1990 revoked the status of the word kilo . The SI system was introduced in 1960 and in 1970 the BIPM started publishing the SI Brochure , which contains all relevant decisions and recommendations by

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552-541: Is the base unit of mass in the International System of Units (SI), having the unit symbol kg . 'Kilogram' means 'one thousand grams ' and is colloquially abbreviated to kilo . The kilogram is an SI base unit , defined ultimately in terms of three defining constants of the SI, namely a specific transition frequency of Cs, the speed of light, and the Planck constant. A properly equipped metrology laboratory can calibrate

598-400: Is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10 when expressed in the unit J⋅s, which is equal to kg⋅m ⋅s , where the metre and the second are defined in terms of c and Δ ν Cs . Defined in term of those units, the kg is formulated as: This definition is generally consistent with previous definitions:

644-455: Is the unit decibel for measuring ratios of power and root-power quantities, such as sound level and electrical amplification. Decimal prefix Decimal multiplicative prefixes have been a feature of all forms of the metric system , with six of these dating back to the system's introduction in the 1790s. Metric prefixes have also been used with some non-metric units. The SI prefixes are metric prefixes that were standardised for use in

690-514: The CGPM concerning units. The SI Brochure states that "It is not permissible to use abbreviations for unit symbols or unit names ...". For use with east Asian character sets, the SI symbol is encoded as a single Unicode character, U+338F ㎏ SQUARE KG in the CJK Compatibility block. The replacement of the International Prototype of the Kilogram (IPK) as the primary standard

736-645: The International System of Units (SI) by the International Bureau of Weights and Measures (BIPM) in resolutions dating from 1960 to 2022. Since 2009, they have formed part of the ISO/IEC 80000 standard. They are also used in the Unified Code for Units of Measure (UCUM). The BIPM specifies twenty-four prefixes for the International System of Units (SI) . The first uses of prefixes in SI date back to

782-646: 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", "grand", or just "k". The financial and general news media mostly use m or M, b or B, and t or T as abbreviations for million, billion (10 ) and trillion (10 ), respectively, for large quantities, typically currency and population. The medical and automotive fields in

828-552: The mass remains within 30 ppm of the mass of one litre of water. The kilogram is the only base SI unit with an SI prefix ( kilo ) as part of its name. The word kilogramme or kilogram is derived from the French kilogramme , which itself was a learned coinage, prefixing the Greek stem of χίλιοι khilioi "a thousand" to gramma , a Late Latin term for "a small weight", itself from Greek γράμμα . The word kilogramme

874-530: The year , equal to exactly 31 557 600  seconds ( ⁠365 + 1  / 4 ⁠  days). The unit is so named because it was the average length of a year in the Julian calendar . Long time periods are then expressed by using metric prefixes with the annum, such as megaannum (Ma) or gigaannum (Ga). The SI unit of angle is the radian , but degrees , as well as arc-minutes and arc-seconds , see some scientific use. Common practice does not typically use

920-437: The 11th CGPM conference in 1960. Other metric prefixes used historically include hebdo- (10 ) and micri- (10 ). Double prefixes have been used in the past, such as micromillimetres or millimicrons (now nanometres ), micromicrofarads (μμF; now picofarads , pF), kilomegatonnes (now gigatonnes ), hectokilometres (now 100  kilometres ) and the derived adjective hectokilometric (typically used for qualifying

966-619: The 1790s, long before the 1960 introduction of the SI. The prefixes, including those introduced after 1960, are used with any metric unit, whether officially included in the SI or not (e.g., millidyne and milligauss). Metric prefixes may also be used with some non-metric units, but not, for example, with the non-SI units of time. The units kilogram , gram , milligram , microgram, and smaller are commonly used for measurement of mass . However, megagram, gigagram, and larger are rarely used; tonnes (and kilotonnes, megatonnes, etc.) or scientific notation are used instead. The megagram does not share

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1012-574: The French word kilo , a shortening of kilogramme , was imported into the English language where it has been used to mean both kilogram and kilometre. While kilo as an alternative is acceptable, to The Economist for example, the Canadian government's Termium Plus system states that "SI (International System of Units) usage, followed in scientific and technical writing" does not allow its usage and it

1058-462: The IPK from 1889 to 2019. In 1960, the metre , previously similarly having been defined with reference to a single platinum-iridium bar with two marks on it, was redefined in terms of an invariant physical constant (the wavelength of a particular emission of light emitted by krypton , and later the speed of light ) so that the standard can be independently reproduced in different laboratories by following

1104-524: The Latin annus ), is commonly used with metric prefixes: ka , Ma, and Ga. Official policies about the use of SI prefixes with non-SI units vary slightly between the International Bureau of Weights and Measures (BIPM) and the American National Institute of Standards and Technology (NIST). For instance, the NIST advises that "to avoid confusion, prefix symbols (and prefix names) are not used with

1150-477: The United States use the abbreviations cc or ccm for cubic centimetres. One  cubic centimetre is equal to one  millilitre . For nearly a century, engineers used the abbreviation MCM to designate a "thousand circular mils " in specifying the cross-sectional area of large electrical cables . Since the mid-1990s, kcmil has been adopted as the official designation of a thousand circular mils, but

1196-404: The astronomical unit is mentioned in the SI standards as an accepted non-SI unit. Prefixes for the SI standard unit second are most commonly encountered for quantities less than one second. For larger quantities, the system of minutes (60 seconds), hours (60 minutes) and days (24 hours) is accepted for use with the SI and more commonly used. When speaking of spans of time,

1242-736: The definition of kilogram after the French Revolution at the end of the 18th century. Several more prefixes came into use, and were recognised by the 1947 IUPAC 14th International Conference of Chemistry before being officially adopted for the first time in 1960. The most recent prefixes adopted were ronna- , quetta- , ronto- , and quecto- in 2022, after a proposal from British metrologist Richard J. C. Brown. The large prefixes ronna- and quetta- were adopted in anticipation of needs for use in data science, and because unofficial prefixes that did not meet SI requirements were already circulating. The small prefixes were also added, even without such

1288-523: The designation MCM still remains in wide use. A similar system is used in natural gas 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, where MMbbl is the symbol for "millions of barrels". This usage of the capital letter M for "thousand" is from Roman numerals , in which M means 1000. Kilogram The kilogram (also spelled kilogramme )

1334-515: The flexibility allowed by official policy in the case of the degree Celsius (°C). NIST states: "Prefix symbols may be used with the unit symbol °C and prefix names 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 with

1380-476: The fuel consumption measures). These are not compatible with the SI. Other obsolete double prefixes included "decimilli-" (10 ), which was contracted to "dimi-" and standardised in France up to 1961. There are no more letters of the Latin alphabet available for new prefixes (all the unused letters are already used for units). As such, Richard J.C. Brown (who proposed the prefixes adopted for 10 and 10 ) has proposed

1426-422: The hectolitre (100 litres). 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. The kilometre, metre, centimetre, millimetre, and smaller units are common. The decimetre is rarely used. The micrometre is often referred to by

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1472-418: The length of the day is usually standardised to 86 400  seconds so as not to create issues with the irregular leap second . Larger multiples of the second such as kiloseconds and megaseconds are occasionally encountered in scientific contexts, but are seldom used in common parlance. For long-scale scientific work, particularly in astronomy , the Julian year or annum (a) is a standardised variant of

1518-429: The metric SI system. Common examples include the megabyte and the decibel . Metric prefixes rarely appear with imperial or US units except in some special cases (e.g., microinch, kilofoot, kilopound ). They are also used with other specialised units used in particular fields (e.g., megaelectronvolt , gigaparsec , millibarn , kilodalton ). In astronomy, geology, and palaeontology, the year , with symbol 'a' (from

1564-453: The older non-SI name micron , which is officially deprecated. In some fields, such as chemistry , the ångström (0.1 nm) has been used commonly instead of the nanometre. The femtometre , used mainly in particle physics, is sometimes called a fermi . For large scales, megametre, gigametre, and larger are rarely used. Instead, ad hoc non-metric units are used, such as the solar radius , astronomical units , light years , and parsecs ;

1610-423: The prefixes formerly used in the metric system have fallen into disuse and were not adopted into the SI. The decimal prefix for ten thousand, myria- (sometimes spelt myrio- ), and the early binary prefixes double- (2×) and demi- ( ⁠ 1 / 2 ⁠ ×) were parts of the original metric system adopted by France in 1795, but were not retained when the SI prefixes were internationally adopted by

1656-500: The reproducible production of new, kilogram-mass prototypes on demand (albeit with extraordinary effort) using measurement techniques and material properties that are ultimately based on, or traceable to, physical constants. Others were based on devices that measured either the acceleration or weight of hand-tuned kilogram test masses and that expressed their magnitudes in electrical terms via special components that permit traceability to physical constants. All approaches depend on converting

1702-477: The risk of confusion that the tonne has with other units with the name "ton". The kilogram is the only coherent unit of the International System of Units that includes a metric prefix. 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 liquids, and the decilitre is used less frequently. Bulk agricultural products, such as grain, beer and wine, often use

1748-440: The time-related unit symbols (names) min (minute), h (hour), d (day); nor with the angle-related symbols (names) ° (degree), ′ (minute), and ″ (second)", whereas the BIPM adds information about the use of prefixes with the symbol as for arcsecond when they state: "However astronomers use milliarcsecond, which they denote mas, and microarcsecond, μas, which they use as units for measuring very small angles." Some of

1794-415: The unit of MK (megakelvin), and molecular cooling may be given with the unit mK (millikelvin). In use the joule and kilojoule are common, with larger multiples seen in limited contexts. In addition, the kilowatt-hour , a composite unit formed from the kilowatt and hour, is often used for electrical energy; other multiples can be formed by modifying the prefix of watt (e.g. terawatt-hour). There exist

1840-604: Was accepted by the 24th conference of the CGPM in October 2011 and further discussed at the 25th conference in 2014. Although the Committee recognised that significant progress had been made, they concluded that the data did not yet appear sufficiently robust to adopt the revised definition, and that work should continue to enable the adoption at the 26th meeting, scheduled for 2018. Such a definition would theoretically permit any apparatus that

1886-515: Was adopted in Great Britain when the word was used for the first time in English in 1795, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with "kilogram" having become by far the more common. UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century

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1932-410: Was capable of delineating the kilogram in terms of the Planck constant to be used as long as it possessed sufficient precision, accuracy and stability. The Kibble balance is one way to do this. As part of this project, a variety of very different technologies and approaches were considered and explored over many years. Some of these approaches were based on equipment and procedures that would enable

1978-594: Was created, it included the " μ " symbol for micro at codepoint 0xB5 ; later, the whole of ISO 8859-1 was incorporated into the initial version of Unicode . Many fonts that support both characters render them identical, but because the micro sign and the Greek lower-case letter have different applications (normally, a Greek letter would be used with other Greek letters, but the micro sign is never used like that), some fonts render them differently, e.g. Linux Libertine and Segoe UI . Most English-language keyboards do not have

2024-525: Was motivated by evidence accumulated over a long period of time that the mass of the IPK and its replicas had been changing; the IPK had diverged from its replicas by approximately 50 micrograms since their manufacture late in the 19th century. This led to several competing efforts to develop measurement technology precise enough to warrant replacing the kilogram artefact with a definition based directly on physical fundamental constants. The International Committee for Weights and Measures (CIPM) approved

2070-520: Was necessary to use some other symbol besides upper and lowercase 'm'. Eventually the Greek letter "μ" was adopted. However, with the lack of a "μ" key on most typewriters, as well as computer keyboards, various other abbreviations remained common, including "mc", "mic", and "u". From about 1960 onwards, "u" prevailed in type-written documents. Because ASCII , EBCDIC , and other common encodings lacked code-points for " μ ", this tradition remained even as computers replaced typewriters. When ISO 8859-1

2116-565: Was written into French law in 1795, in the Decree of 18 Germinal , which revised the provisional system of units introduced by the French National Convention two years earlier, where the gravet had been defined as weight ( poids ) of a cubic centimetre of water, equal to 1/1000 of a grave . In the decree of 1795, the term gramme thus replaced gravet , and kilogramme replaced grave . The French spelling

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