Millimetre

(Redirected from Millimeter)

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 systemSI
Unit ofLength
Symbolmm
Named afterFrom 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
Different lengths with respect to the electromagnetic spectrum. The microwave spans from 1 metre to 1 millimetre.

- 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 5127 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 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

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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

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To 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

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- 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

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References

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  1. ^ "17th General Conference on Weights and Measures (1983), Resolution 1". International Bureau of Weights and Measures. Retrieved 3 December 2013.
  2. ^ "CJK Compatibility" (PDF). unicode.org. Retrieved 3 December 2013.
  3. ^ "How do I read a ruler?". onlineconversion.com. Retrieved 3 December 2013.
  4. ^ "Accuracy of Calipers". TresnaInstrument.com. Retrieved 3 December 2013.
  5. ^ Huang, Kao-Cheng; Wang, Zhaocheng (2011). Millimeter Wave Communication Systems. John Wiley & Sons. ISBN 9781118102756.
  6. ^ "How Small Can the Naked Eye See?". Focus Magazine. Retrieved 3 December 2013.
  7. ^ Sherlis, Juliya (2001). Elert, Glenn (ed.). "Thickness of a piece of paper". The Physics Factbook. Retrieved 2022-01-21.