The millimetre (SI symbol: mm; international spelling) or millimeter (American spelling) is a unit of length in the International System of Units (SI), equal to one thousandth of a metre, the SI base unit of length.
| millimetre | |
|---|---|
 Ruler with millimetre and centimetre marks | |
| General information | |
| Unit system | SI |
| Unit of | Length |
| Symbol | mm |
| Named after | From metric prefix mille (Latin for "one thousand") and the metre |
| Conversions | |
| 1 mm in ... | ... is equal to ... |
| micrometres | 1000 μm = 1000 micrometres |
| centimetres | 0.1 cm |
| metres | 0.001 m |
| kilometres | 1×10−6 km |
| inches | 0.039370 in |
| feet | 0.0032808 ft |
- 1 metre = 1000 millimetres - 1 centimetre = 10 millimetres
One millimetre is also equal to: - 1000 micrometres - 1000000 nanometres
Since an inch is officially defined as exactly 25.4 millimetres, 1 millimetre is precisely 5⁄127 inches (≈ 0.03937 inches).
Definition
editSince 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".[1]
A millimetre, being 1/1000 of a metre, is the distance light travels in 1/299792458000 of a second.
Informal terminology
editThe term "mil" is sometimes used colloquially for millimetre. However, in the United States, "mil" traditionally means a thousandth of an inch, which may cause confusion.
Unicode symbols
editTo support layout compatibility with East Asian scripts (CJK), Unicode includes square symbols for:
- Millimetre – U+339C ㎜ SQUARE MM
- Square millimetre – U+339F ㎟ SQUARE MM SQUARED
- Cubic millimetre – U+33A3 ㎣ SQUARE MM CUBED[2]
These symbols are often used in Japanese typography to align unit symbols with text characters.
Measurement
edit- On a standard metric ruler, the smallest divisions are typically millimetres.[3] - Precision engineering rulers may show increments of 0.5 mm. - Digital calipers often measure to 0.01 mm accuracy.[4]
Examples: - Microwaves with a frequency of 300 GHz have a wavelength of 1 mm. - Using frequencies from 30–300 GHz for millimetre-wave communications allows high-speed data transfer (e.g., 10 Gbps).[5] - The smallest visible object to the human eye is around 0.02–0.04 mm (e.g., a thin human hair).[6] - A typical sheet of paper is between 0.07 mm and 0.18 mm thick; copy paper is about 0.1 mm.[7]
See also
edit
References
edit- ^ "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.