Length units
Enter a value in any field — all other length units update instantly. Metric, imperial, nautical mile.
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Converter
Digits
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Reference relationships
how length units relate to each other03
About length units
Three systems of length measurement coexist: metric (SI), imperial and nautical. Metric is used almost everywhere, imperial — in the USA, UK and Canada, and the nautical mile — in aviation and maritime navigation regardless of country.
Screen diagonals, pipe diameters and bicycle tyre sizes are in inches almost everywhere — including Russia. Aviation altitude follows the ICAO standard in feet: FL350 = 35 000 ft ≈ 10 670 m.
Metric system (SI)
Global1 km = 1 000 m = 100 000 cm = 10⁶ mm
Based on the metre and decimal powers. Adopted by most countries, international standard in science and trade. The metre is defined by the speed of light: the distance light travels in a vacuum in 1/299 792 458 of a second.
Imperial system
US / UK1 mi = 1 760 yd = 5 280 ft = 63 360 in
Developed in Britain, based on human proportions: an inch — width of a thumb, a foot — length of a foot, a yard — from the king's nose to his fingertips. Only the USA, Liberia and Myanmar still officially use it.
Nautical mile
ICAO / IMO1 nmi = 1 852 m · 1 knot = 1 nmi/h
International standard in aviation and at sea. Equals one arcminute of Earth's meridian. A knot is speed: 1 nmi per hour. Not to be confused with a statute mile — the nautical mile is 243 m longer.
Where each is used
screen — in · height — cm or ft · pipes — in
Screen diagonals and pipe diameters are in inches everywhere (even in Russia). Human height is in centimetres in Europe / Russia, in feet in the USA / UK. Aviation uses feet for altitude regardless of country.