my-server
← Wiki Redirected from Millimeters

Millimetre

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:

Since an inch is officially defined as exactly 25.4 millimetres, 1 millimetre is precisely inches (≈ 0.03937 inches).

Definition

Since 1983, the metre has been defined as "the length of the path travelled by light in vacuum during a time interval of of a second".

A millimetre, being of a metre, is the distance light travels in 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 –
  • Square millimetre –
  • Cubic millimetre –

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.
  • Precision engineering rulers may show increments of 0.5 mm.
  • Digital calipers often measure to 0.01 mm accuracy.

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).
  • The smallest visible object to the human eye is around 0.02–0.04 mm (e.g., a thin human hair).
  • A typical sheet of paper is between 0.07 mm and 0.18 mm thick; copy paper is about 0.1 mm.

See also

References