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Unit of length

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A unit of length is a way of measuring length or distance.

Common units of length in the International System of Units (SI) are:

But there are a lot of units that do not fit in the SI-System:

Common Imperial units and U.S. customary units of length include:

  • inch (25.4 mm)
  • mil (one thousandth of an inch, one thou)
  • foot (0.3048 m, 12 inches)
  • yard (0.9144 m)
  • (terrestrial) mile (1609.344 m)

In addition, the following are used by mariners:

Surveyors in the United States continue to use:

  • chain (~20.1m)
  • rod (also called pole or perch) (~5 m)

Horse racing keeps alive:

Astronomical measure uses:

Physics also uses:

Old units of distance are:

In everyday conversation, and in informal literature, it is common to see lengths measured in units of objects of which everyone knows the approximate width. Common examples are:

  • Football field (generally around 110 metres, depending on the country)
  • Widths of a human hair (around 80 micrometres)