The millimetre (International spelling as used by the International
Bureau of Weights and Measures; SI unit symbol mm) or millimeter
(American spelling) is a unit of length in the metric system, equal to
one thousandth of a metre, which is the
SI base unit
Since 1983, the metre has been defined as "the length of the path
travelled by light in vacuum during a time interval of
1/7008299792458000000♠299792458 of a second". A millimetre,
1/1000 of a metre, is therefore the distance travelled by light in
1/7011299792458000000♠299792458000 of a second.
millimetre (㎜) - code U+339C square millimetre (㎟) - code U+339F cubic millimetre (㎣) - code U+33A3
In Japanese typography, these square symbols were historically used for laying out unit symbols without distorting the grid layout of text characters. Measurement On a metric ruler, the smallest measurements are normally millimetres. High-quality engineering rules may be graduated in increments of 0.5 mm. Digital Vernier callipers are commonly capable of reading increments as small as 0.01 mm. Microwaves with a frequency of 300 GHz have a wavelength of 1 mm. Using wavelengths between 30 GHz and 300 GHz for data transmission, in contrast to the 300 MHz to 3 GHz normally used in mobile devices, has the potential to allow data transfer rates of 10 gigabits per second. The smallest distances the human eye can resolve is around 0.02 to 0.04 mm, approximately the width of a human hair. A sheet of paper is typically between 0.07 mm and 0.18 mm thick, with ordinary printer paper or copy paper approximately a tenth of a millimetre thick. See also
Look up millimetre in Wiktionary, the free dictionary.
Metric system Orders of magnitude (length) Submillimeter
^ "17th General Conference on Weights and Measures (1983), Resolution 1". International Bureau of Weights and Measures. Retrieved 3 December 2013. ^ a b c " CJK Compatibility" (PDF). unicode.org. Retrieved 3 December 2013. ^ "How do I read a ruler?". onlineconversion.com. Retrieved 3 December 2013. ^ "Accuracy of Calipers". TresnaInstrument.com. Retrieved 3 December 2013. ^ Huang, Kao-Cheng; Wang, Zhaocheng (2011). Millimeter Wave Communication Systems. ISBN 9781118102756. ^ "How Small Can the Naked Eye See?". Focus Magazine. Retrieved 3 December 2013. ^ "Thickness of a Piece of Paper". hypertextbook.com. Retrieved 3 December 2013.
v t e
SI units of length
From smallest to largest (left to right). Commonly used units shown in bold italics.
yoctometre (1×10−24 m) zeptometre attometre femtometre picometre nanometre micrometre millimetre centimetre decimetre metre (m) decametre hectometre kilometre megametre gigametre terametre petametre exametre zettametre yott