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A centimetre (international spelling as used by the International Bureau of Weights and Measures; symbol cm) or centimeter (American spelling) 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.[1] The centimetre was the base unit of length in the now deprecated centimetre–gram–second (CGS) system of units.

A carpenter's ruler with centimetre divisions
General information
Unit systemmetric
Unit oflength
1 cm in ...... is equal to ...
   SI units   10 mm
   imperial & US system   ~0.3937 in

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 lengthEdit

1 centimetre = 10 millimetres
= 0.01 metres
= 0.393700787401574803149606299212598425196850 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 usesEdit

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 [2]
  • in the CGS system, the centimetre is used to measure capacitance, where 1 cm of capacitance = 1.113×10−12 farads[3]
  • 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 symbolsEdit

For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:[4]

  • 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.

See alsoEdit


  1. ^ "Decimal multiples and submultiples of SI units". Bureau International des Poids et Mesures. 2014. Retrieved 5 July 2015.
  2. ^ Rain Measurement, Rain Gauge, Wireless Rain Gauge, Rain Gage, Rain Gauge Data
  3. ^ Capacitance - from Eric Weisstein's World of Physics
  4. ^ CJK Compatibility excerpt from The Unicode Standard, Version 10.0.