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| unit = [[metre]] (m)
| otherunits = see [[unit of length]]
| symbols =
| dimension =
| extensive = yes
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'''Length''' is a measure of [[distance]]. In the [[International System of Quantities]], length is a [[quantity]] with [[Dimension (physical quantity)|dimension]] distance. In most [[
Length is commonly understood to mean the most extended [[size|dimension]] of a fixed object.<ref name=":0">{{Cite
Various terms for the length of a fixed object are used, and these include [[height]], which is vertical length or vertical extent,
Length is the measure of one spatial dimension, whereas [[area]] is a measure of two dimensions (length squared) and [[volume]] is a measure of three dimensions (length cubed).
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Measurement has been important ever since humans settled from nomadic lifestyles and started using building materials, occupying land and trading with neighbours. As trade between different places increased, the need for standard units of length increased. And later, as society has become more technologically oriented, much higher accuracy of measurement is required in an increasingly diverse set of fields, from micro-electronics to interplanetary ranging.<ref>History of Length Measurement, [http://resource.npl.co.uk/docs/educate_explore/posters/bg_historyoflength_poster.pdf National Physical Laboratory] {{Webarchive|url=https://web.archive.org/web/20131126043209/http://resource.npl.co.uk/docs/educate_explore/posters/bg_historyoflength_poster.pdf |date=2013-11-26 }}</ref>
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The [[area]] of a [[rectangle]] is defined to be length × width of the rectangle. If a long thin rectangle is stood up on its short side then its area could also be described as its height × width.
The [[volume]] of a [[
The [[perimeter]] of a [[polygon]] is the sum of the lengths of its [[Edge (geometry)|sides]].
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== Units ==
{{Main|Unit of length}}
In the physical sciences and engineering, when one speaks of {{em|[[unit of length|units of length]]}}, the word {{em|length}} is synonymous with [[distance]]. There are several [[Units of measurement|units]] that are used to [[Measurement|measure]] length. Historically, units of length may have been derived from the lengths of human body parts, the distance
In the [[International System of Units]] (SI), the [[SI base unit|base unit]] of length is the [[metre]] (symbol, m)
Units used to denote distances in the vastness of space, as in [[astronomy]], are much longer than those typically used on Earth (metre or
Units used to denote sub-atomic distances, as in [[nuclear physics]], are much smaller than the
== See also ==
* [[Arc length]]
* [[List of humorous units of measurement#Length|Humorous units of length]]
* [[Length measurement]]
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