Editing Metric prefix (section)

== Usage ==

=== Examples ===
* The mass of an [[electron]] is about 1&nbsp;rg (rontogram).<ref name="earth-electron"/>{{efn|{{physconst|me|symbol=yes}}. Converting to grams gives {{val|9.1093837015|e=-28|u=g}}. Rounding to the nearest power of ten gives {{val|1|e=-27|u=g}}, or 1&nbsp;rg.}}
* The mass of 1 litre of [[water]] is about 1&nbsp;kg (kilogram).<ref>{{Cite web
| url = https://www.britannica.com/science/kilogram
| title = Kilogram &#124; mass, weight, SI unit &#124; Britannica
| date = 15 March 2024
}}</ref>
* The mass of the [[Earth]] is about 6&nbsp;Rg (ronnagrams).<ref name="earth-electron"/>
* The mass of [[Jupiter]] is about 2&nbsp;Qg (quettagrams).<ref name="earth-electron"/>

=== Examples of powers of units with metric prefixes<span class="anchor" id="Metric powers"></span> ===
* 1&nbsp;km<sup>2</sup> means one [[square kilometre]], or the [[area]] of a [[Square (geometry)|square]] of {{val|1000|u=m}} by {{val|1000|u=m}}. In other words, an area of {{val|1000000}} [[square metre]]s and not {{val|1000}} [[square metre]]s.
* 2&nbsp;Mm<sup>3</sup> means two cubic [[megametre]]s, or the [[volume]] of two [[cube]]s of {{val|1000000|u=m}} by {{val|1000000|u=m}} by {{val|1000000|u=m}}, i.e. {{val|2|e=18|u=m3}}, and not {{val|2000000}} [[cubic metre]]s ({{val|2|e=6|u=m3}}).

=== Examples with prefixes and powers ===
* {{val|5|u=mV}} × {{val|5|u=mA}} = {{val|5|e=-3|u=V}} × {{val|5|e=-3|u=A}} = {{val|25|e=-6|u=V⋅A}} = {{val|25|u=uW}}.
* {{val|5.00|u=mV}} + {{val|10|u=uV}} = {{val|5.00|u=mV}} + {{val|0.01|u=mV}} = {{val|5.01|u=mV}}.
* {{val|5|u=cm}} =&nbsp;{{val|5|e=-2|u=m}} =&nbsp;{{nowrap|5 × 0.01 m}} =&nbsp;0.05&nbsp;m.
* {{val|9|u=km2}} =&nbsp;{{nowrap|9 × (10<sup>3</sup> m)<sup>2</sup>}} =&nbsp;{{nowrap|9 × (10<sup>3</sup>)<sup>2</sup> × m<sup>2</sup>}} =&nbsp;{{val|9|e=6|u=m2}} =&nbsp;{{nowrap|9 × {{val|1000000|u=m2}}}} =&nbsp;{{val|9000000|u=m2}}.
* 3&nbsp;MW =&nbsp;{{val|3|e=6|u=W}} =&nbsp;3&nbsp;×&nbsp;{{val|1000000|u=W}} = {{val|3000000|u=W}}.

=== Micro symbol ===
{{main|Micro-}}
When ''mega'' and ''micro'' were adopted in 1873, three prefixes existed starting with "m". It was necessary to use a symbol other than upper and lowercase 'm'. Eventually the Greek letter "μ" was adopted.

With the lack of a "μ" key on most typewriters, as well as computer keyboards, various other abbreviations remained common, including "mc", "mic", ''M'', and "u".

From about 1960 onwards, "u" prevailed in type-written documents.{{efn|
Sometimes the symbol 'u' is marked by adding a downstroke using a pen or pencil, or a slash '/u'.
}} Because [[ASCII]], [[EBCDIC]], and other common encodings lacked code-points for "{{math|μ}}", this tradition remained even as computers replaced typewriters.

When [[ISO 8859-1]] was created, it included the "{{math|μ}}" symbol for ''micro'' at codepoint {{code|0xB5}}; later, the whole of ISO 8859-1 was incorporated into the initial version of [[Unicode]]. Many fonts that support both characters render them identically, 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]].{{cn|date=October 2024}}

==== Keyboard entry ====
Most English-language keyboards do not have a "{{math|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.

; For all keyboard layouts
:* On [[Microsoft Windows]] systems,
:** arbitrary Unicode codepoints can be entered in decimal with: {{key press|Alt}} sustained, {{key press|0}} {{key press|1}} {{key press|8}} {{key press|1}}, and releasing {{key press|Alt}}. A leading "0" is required<br/> (this registers as the corresponding Unicode hexadecimal code-point, 0xB5 = 181.), or
:** arbitrary Unicode codepoints can be entered in hexadecimal as: {{key press|Alt|+}}{{key press|b}}{{key press|5}}<br/> (up to 5&nbsp;hexadecimal characters, not counting the leading '+', upper or lower case), or
:** in the tradition of MS-DOS, [[CP437|IBM code page 437]] one can also enter old code-points in decimal: {{key press|Alt|2}}{{key press|3}}{{key press|0}}<br/> (the leading zero must be omitted);
:* On [[Linux]] systems,
:** under X11, when a [[Compose key]] has been enabled: {{key press|Compose}}{{key press|m}}{{key press|u}}
:** under X11, with ''ibus'' version 1.5.19 (or higher) active, and a non-composing input method selected<!-- e.g. mozc-Japanese-Hiragana mode overrides keystrokes like 'u','b',SPACE to provide the hiragana/kanji composition feature -->: The default keybinding for starting codepoint input is {{key press|Ctrl|Shift|u}}. The key sequence {{key press|Ctrl|Shift|u}} {{key press|b}} {{key press|5}} {{key press|space}} then produces U+00B5, the micro sign.
:** on the VGA console's virtual terminals like tty1: arbitrary Unicode codepoints can be entered in decimal as: {{key press|Alt}} sustained, {{key press|1}} {{key press|8}} {{key press|1}}, and releasing {{key press|Alt}}. A leading "0" is not required.

; For QWERTY keyboard layouts
:* On [[Linux]] systems,
:** code-point U+00b5 can be entered as {{key press|right-alt|m}} (provided the right [[alt key]] is configured to act as {{code|AltGr}}).
:* On [[MacOS]] systems, code-point U+00b5 can be entered as either {{key press|Opt|m}} or {{key press|Opt|Y}}.

=== Typesetting in LaTeX ===

The [[LaTeX]] typesetting system features an ''SIunitx'' package in which the units of measurement are spelled out, for example,
<br/> <code>\qty{3}{\tera\hertz}</code> formats as "3&nbsp;THz".<ref>{{citation
| title = LaTeX Cookbook
| first = Stefan
| last = Kottwitz
| pages = 158–9
| date = 2015-10-28
| publisher = Packt Publishing Ltd
| isbn = 978-1-78439-630-5
}}</ref>