A carpenter's ruler with centimetre divisions
|SI units||10 mm|
|imperial & US system||~0.3937 in|
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 . 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.
In addition to its use in the measurement of length, the centimetre is used:
They are mostly used only with East Asian fixed-width CJK fonts, because they are equal in size to one Chinese character.