Editing Metric prefix (section)

== List of SI prefixes ==
{{Redirect-several|Atto|Exa|Peta|Pico|Quetta|Ronto|Tera}}
{{Redirect-multi|5|Femto|Ronna-|Yocto|Yotta|Zepto|the character|Griffith (Berserk)|the name|Ronna|the Linux Foundation open-source project|Yocto Project|the prize-linked savings account|Yotta Technologies|the Finnish musician|Yotto|similar terms|Yota (disambiguation)|the Indian Q-commerce company|Zepto (company)}}
The BIPM specifies twenty-four [[International System of Units#Prefixes|prefixes for the International System of Units (SI)]].
{{Anchor|SI prefixes table}}
{{SI prefixes (infobox)}}

The first uses of prefixes in SI date back to 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 [[International Union of Pure and Applied Chemistry|IUPAC]] 14th International Conference of Chemistry<ref>{{Cite work
| publisher = [[International Union of Pure and Applied Chemistry|IUPAC]]
| title = Comptes rendus de la Quatorzième Conférence
| location = London
| date = 24 July 1947
| language = fr
| url = https://archive.org/details/iupaccomptesrend14iupa
}}</ref> before being officially adopted for the first time in 1960.<ref name="res12">{{Cite web
| title = Resolution 12 of the 11th meeting of the CGPM
| publisher = Bureau International des Poids et Mesures
| website = Bipm.org
| year = 1960
| url = http://www.bipm.org/en/CGPM/db/11/12/
| url-status = deviated
| archive-url = https://archive.today/20130213132948/http://www.bipm.org/en/CGPM/db/11/12/
| archive-date = 2013-02-13
| access-date = 2023-09-12
}}</ref>

The most recent prefixes adopted were ''ronna'', ''quetta'', ''ronto'', and ''quecto'' in 2022, after a proposal from British metrologist Richard J. C. Brown (since before 2022, Q/q and R/r were the only Latin letters available for abbreviations, all other Latin letters are either already used for other prefixes ([[atto-|a]], [[centi-|c]], [[deci-|d]], [[exa-|E]], [[femto-|f]], [[giga-|G]], [[hecto-|h]], [[kilo-|k]], [[mega-|M]], [[milli-|m]], [[nano-|n]], [[peta-|P]], [[pico-|p]], [[tera-|T]], [[yotta-|Y]], [[yocto-|y]], [[zetta-|Z]], [[zepto-|z]]) or already used for [[SI units]] (including: [[SI base unit]]s, [[SI derived unit]]s, [[Non-SI units mentioned in the SI]]) ([[ampere|A]], [[bel (unit)|B]], [[coulomb|C]], [[day|d]], [[farad|F]], [[gram|g]], [[henry (unit)|H]], [[hour|h]], [[joule|J]], [[kelvin|K]], [[litre|L]], [[metre|m]], [[newton (unit)|N]], [[siemens (unit)|S]], [[second|s]], [[tesla (unit)|T]], [[tonne|t]], [[unified atomic mass unit|u]], [[Volt|V]], [[Watt|W]]) or easily confused with mathematical operators (I and l are easily confused with 1, O and o are easily confused with 0, X and x are easily confused with ×)). 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 a driver, in order to maintain symmetry.<ref name="earth-electron">{{citation
| title = Earth weighs in at six ronnagrams as new prefixes picked for big and small
| url = https://www.theguardian.com/science/2022/nov/18/earth-six-ronnagrams-new-prefixes-big-and-small
| date = 2022-11-18
| first = Ian
| last = Sample
| newspaper = [[The Guardian]]
| access-date = 2022-12-14
}}</ref>

The prefixes from ''peta'' to ''quetta'' are based on the Ancient Greek or Ancient Latin numbers from 5 to 10, referring to the 5th through 10th powers of 10<sup>3</sup>. 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.

=== Rules ===
* The symbols for the units of measure are combined with the symbols for each prefix name. The SI symbols for kilometre, kilogram, and kilowatt, for instance, are km, kg, and kW, respectively. (The symbol for ''kilo'' is k.) Except for the early prefixes of ''kilo'', ''hecto'', and ''deca'', the symbols for the prefixes for multiples are uppercase letters, and those for the prefixes for submultiples are lowercase letters.<ref>{{Cite web
| title = Metric Prefixes and SI Units
| series = tutorials
| website = learn.sparkfun.com
| url = https://learn.sparkfun.com/tutorials/metric-prefixes-and-si-units/all
| access-date = 26 January 2020
}}</ref>
* All of the metric prefix symbols are made from upper- and lower-case [[Latin alphabet|Latin letters]] except for the symbol for ''micro'', which is uniquely a Greek letter [[mu (letter)|{{math|μ}}]].{{efn|For [[ASCII]] compatibility in general text usage, {{math|μ}} is frequently substituted with the Latin letter ''u''.}}
* The prefix symbols are always prepended to the symbol for the unit without any intervening space or punctuation.<ref>{{Cite web
| url = https://physics.nist.gov/cuu/Units/checklist.html
| title = SI Unit rules and style conventions checklist
| publisher = [[National Institute of Standards and Technology|NIST]]
| website = nist.gov
| date = September 2004
| orig-date = February 1998
}}</ref> This distinguishes a prefixed unit symbol from the product of unit symbols, for which a space or mid-height dot as separator is required. So, for instance, while 'ms' means millisecond, 'm&nbsp;s' or 'm·s' means metre-second.
* Prefixes corresponding to an integer power of one thousand are generally preferred; the prefixes corresponding to tens (deci-, deca-) and hundreds (centi-, hecto-) are less common and are disfavoured in certain fields. Hence, 100&nbsp;m is preferred over 1&nbsp;hm (hectometre) or 10&nbsp;dam (decametres). The prefixes ''deci-'' and ''centi-'', and less frequently ''hecto'' and ''deca'', are generally used for informal purposes; the centimetre (cm) is especially common. 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".<ref>{{Cite report
| title = Metric Design Guide
| date = September 1995
| id = PBS-PQ260
| series = Public Buildings Service
| publisher = U.S. [[General Services Administration]]
| via = National Institute of Building Sciences
| url = http://wbdg.org/ccb/GSAMAN/mdg.pdf
| access-date = 21 April 2018
| archive-url = https://web.archive.org/web/20111215115519/http://wbdg.org/ccb/GSAMAN/mdg.pdf
| archive-date = 15 December 2011
}}</ref> These prefixes are also commonly used to create metric units corresponding to older conventional units, for example [[hectare]]s and [[hectopascal]]s.
* Prefixes may not be used in combination on a single symbol. This includes the case of the base unit kilogram, which already contains a prefix. For example, milligram (mg) is used instead of microkilogram (μkg).
* During mathematical operations, prefixes are treated as multiplicative factors. For example, 5&nbsp;km is treated as 5000&nbsp;m, which allows all quantities based on the same unit to be [[Conversion of units#Factor–label method|factored together]] even if they have different prefixes.
* A prefix symbol attached to a unit symbol is included when the unit is raised to a power. For example, 1&nbsp;km<sup>2</sup> denotes 1&nbsp;km&nbsp;×&nbsp;1&nbsp;km = 10<sup>6</sup>&nbsp;m<sup>2</sup>, not 10<sup>3</sup>&nbsp;m<sup>2</sup>.