Millimetre
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| millimetre | |
|---|---|
| Lua error in package.lua at line 80: module 'Module:InfoboxImage/data' not found. 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 |
| centimetres | Page Template:Sfrac/styles.css has no content.1/10 |
| metres | Page Template:Sfrac/styles.css has no content.1/1000 |
| kilometres | Page Template:Sfrac/styles.css has no content.1/1 000 000 |
| decimetres | Page Template:Sfrac/styles.css has no content.1/100 |
| inches | 0.039370 in |
| feet | 0.0032808 ft |
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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.
- 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 Page Template:Fraction/styles.css has no content.5⁄127 inches (≈ 0.03937 inches).
Definition
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Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of Page Template:Sfrac/styles.css has no content.1/299792458 of a second".[1]
A millimetre, being Page Template:Sfrac/styles.css has no content.1/1000 of a metre, is the distance light travels in Page Template:Sfrac/styles.css has no content.1/299 792 458 000 of a second.
Informal terminology
The 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
To support layout compatibility with East Asian scripts (CJK), Unicode includes square symbols for:
- Millimetre – Page Template:Mono/styles.css has no content.U+339C ㎜ Script error: No such module "Unicode data".
- Square millimetre – Page Template:Mono/styles.css has no content.U+339F ㎟ Script error: No such module "Unicode data".
- Cubic millimetre – Page Template:Mono/styles.css has no content.U+33A3 ㎣ Script error: No such module "Unicode data".[2]
These symbols are often used in Japanese typography to align unit symbols with text characters.
Measurement
- 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, such as 10 Gbps.[5]
- The smallest visible object to the human eye is around 0.02–0.04 mm, such as 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]
- Mechanical pencil leads are commonly produced in 0.5 mm and 0.7 mm sizes.
- Printed circuit boards, automotive components and precision-machined engineering parts are frequently specified using millimetres.
Millimetres are also commonly converted into imperial units such as inches for engineering, manufacturing, construction and international product specifications. One inch is defined as exactly 25.4 millimetres.[8][9]
Additional metric and imperial conversion references:
- SI Units – NIST
- Millimetres to inches converter
- Inches to millimetres converter
- International System of Units (BIPM)
- Engineering Toolbox
See also
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References
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- ^ Page Module:Citation/CS1/styles.css has no content."17th General Conference on Weights and Measures (1983), Resolution 1". International Bureau of Weights and Measures. Retrieved 3 December 2013.
- ^ Page Module:Citation/CS1/styles.css has no content."CJK Compatibility" (PDF). unicode.org. Retrieved 3 December 2013.
- ^ Page Module:Citation/CS1/styles.css has no content."How do I read a ruler?". onlineconversion.com. Retrieved 3 December 2013.
- ^ Page Module:Citation/CS1/styles.css has no content."Accuracy of Calipers". TresnaInstrument.com. Retrieved 3 December 2013.
- ^ Page Module:Citation/CS1/styles.css has no content.Huang, Kao-Cheng; Wang, Zhaocheng (2011). Millimeter Wave Communication Systems. John Wiley & Sons. ISBN 9781118102756.
- ^ Page Module:Citation/CS1/styles.css has no content."How Small Can the Naked Eye See?". Focus Magazine. Retrieved 3 December 2013.
- ^ Page Module:Citation/CS1/styles.css has no content.Sherlis, Juliya (2001). Elert, Glenn (ed.). "Thickness of a piece of paper". The Physics Factbook. Retrieved 2022-01-21.
- ^ Page Module:Citation/CS1/styles.css has no content."SI Units – Length". National Institute of Standards and Technology. Retrieved 24 May 2026.
- ^ Page Module:Citation/CS1/styles.css has no content."Millimetres to Inches Conversion Reference". WhatsThisIn. Retrieved 24 May 2026.
