The millimetre (international spelling; SI unit symbol mm) or millimeter (American spelling) is a unit of length in the International System of Units (SI), equal to one thousandth of a metre, which is the SI base unit of length. Therefore, there are one thousand millimetres in a metre. There are ten millimetres in a centimetre.
| millimetre | |
|---|---|
 Ruler with millimetre and centimetre marks | |
| General information | |
| Unit system | SI |
| Unit of | Length |
| Symbol | mm |
| Named after | The metric prefix mille (Latin for "one thousand") and the metre |
| Conversions | |
| 1 mm in ... | ... is equal to ... |
| micrometres | 1×103 μm = 1000 μm |
| centimetres | 1×10−1 cm = 0.1 cm |
| metres | 1×10−3 m = 0.001 m |
| kilometres | 1×10−6 km |
| inches | 0.039370 in |
| feet | 0.0032808 ft |
One millimetre is equal to 1000 micrometres or 1000000 nanometres. Since an inch is officially defined as exactly 25.4 millimetres, a millimetre is equal to exactly 5⁄127 (≈ 0.03937) of an inch.
Definition
Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of 1/299792458 of a second". A millimetre, 1/1000 of a metre, is therefore the distance travelled by light in 1/299792458000 of a second.
Informal terminology
A common shortening of millimetre in spoken English is "mil". This can cause confusion in the United States, where "mil" traditionally means a thousandth of an inch.
Unicode symbols
For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:
- millimetre - U+339C ㎜ SQUARE MM
- square millimetre - U+339F ㎟ SQUARE MM SQUARED
- cubic millimetre U+33A3 ㎣ SQUARE MM CUBED
In Japanese typography, these square symbols are 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 rulers may be graduated in increments of 0.5 mm. Digital 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 frequencies 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 dimension the human eye can resolve is around 0.02 to 0.04 mm, approximately the width of a thin 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 0.1 mm thick.
See also
- Metric system
- Orders of magnitude (length)
- Submillimetre astronomy
References
- "17th General Conference on Weights and Measures (1983), Resolution 1". International Bureau of Weights and Measures. Retrieved 3 December 2013.
- "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. John Wiley & Sons. ISBN 9781118102756.
- "How Small Can the Naked Eye See?". Focus Magazine. Retrieved 3 December 2013.
- Sherlis, Juliya (2001). Elert, Glenn (ed.). "Thickness of a piece of paper". The Physics Factbook. Retrieved 2022-01-21.
The millimetre international spelling SI unit symbol mm or millimeter American spelling is a unit of length in the International System of Units SI equal to one thousandth of a metre which is the SI base unit of length Therefore there are one thousand millimetres in a metre There are ten millimetres in a centimetre millimetreRuler with millimetre and centimetre marksGeneral informationUnit systemSIUnit ofLengthSymbolmmNamed afterThe metric prefix mille Latin for one thousand and the metreConversions1 mm in is equal to micrometres 1 103 mm 1000 mm centimetres 1 10 1 cm 0 1 cm metres 1 10 3 m 0 001 m kilometres 1 10 6 km inches 0 039370 in feet 0 0032808 ftDifferent lengths as in respect to the electromagnetic spectrum measured by the metre and its derived scales The microwave is between 1 meter to 1 millimeter One millimetre is equal to 1000 micrometres or 1000 000 nanometres Since an inch is officially defined as exactly 25 4 millimetres a millimetre is equal to exactly 5 127 0 03937 of an inch DefinitionSince 1983 the metre has been defined as the length of the path travelled by light in vacuum during a time interval of 1 299792 458 of a second A millimetre 1 1000 of a metre is therefore the distance travelled by light in 1 299792 458 000 of a second Informal terminologyA common shortening of millimetre in spoken English is mil This can cause confusion in the United States where mil traditionally means a thousandth of an inch Unicode symbolsFor the purposes of compatibility with Chinese Japanese and Korean CJK characters Unicode has symbols for millimetre U 339C SQUARE MM square millimetre U 339F SQUARE MM SQUARED cubic millimetre U 33A3 SQUARE MM CUBED In Japanese typography these square symbols are used for laying out unit symbols without distorting the grid layout of text characters MeasurementOn a metric ruler the smallest measurements are normally millimetres High quality engineering rulers may be graduated in increments of 0 5 mm Digital 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 frequencies 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 dimension the human eye can resolve is around 0 02 to 0 04 mm approximately the width of a thin 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 0 1 mm thick See alsoLook up millimetre in Wiktionary the free dictionary Metric system Orders of magnitude length Submillimetre astronomyReferences 17th General Conference on Weights and Measures 1983 Resolution 1 International Bureau of Weights and Measures Retrieved 3 December 2013 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 John Wiley amp Sons ISBN 9781118102756 How Small Can the Naked Eye See Focus Magazine Retrieved 3 December 2013 Sherlis Juliya 2001 Elert Glenn ed Thickness of a piece of paper The Physics Factbook Retrieved 2022 01 21
