Centimetre

A centimetre (international spelling) or centimeter (American spelling) (SI symbol cm) is a unit of length in the metric system, equal to one hundredth of a metre, centi being the SI prefix for a factor of $1⁄100$. The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units.

Though for many physical quantities, SI prefixes for factors of 103—like milli- and kilo-—are often preferred by technicians, the centimetre remains a practical unit of length for many everyday measurements. A centimetre is approximately the width of the fingernail of an average adult person.

Equivalence to other units of length



 * rowspan=4 valign=top|1 centimetre
 * = 10 millimetres
 * = 0.01 metres
 * = 0. 39370078740157480314960629921259842519685 inches
 * (There are exactly 2.54 centimetres in one inch.)
 * }
 * = 0. 39370078740157480314960629921259842519685 inches
 * (There are exactly 2.54 centimetres in one inch.)
 * }
 * }

One millilitre is defined as one cubic centimetre, under the SI system of units.

Other uses
In addition to its use in the measurement of length, the centimetre is used:
 * sometimes, to report the level of rainfall as measured by a rain gauge
 * in the CGS system, the centimetre is used to measure capacitance, where 1 cm of capacitance = $1.113$ farads
 * in maps, centimetres are used to make conversions from map scale to real world scale (kilometres)
 * to represent second moment of areas (cm4)
 * as the inverse of the kayser, a CGS unit, and thus a non-SI metric unit of wavenumber: 1 kayser = 1 wave per centimetre; or, more generally, (wavenumber in kaysers) = 1/(wavelength in centimetres). The SI unit of wavenumber is the inverse metre, m−1.

Unicode symbols
For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:
 * centimetre (㎝) – code 339D
 * square centimetre (㎠) – code 33A0
 * cubic centimetre (㎤) – code 33A4

They are mostly used only with East Asian fixed-width CJK fonts, because they are equal in size to one Chinese character.

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