Length converter

Ten units of length, from thou to nautical miles, all converted at once. The inch, foot, yard and mile are exact multiples of the metre by definition, so nothing here is approximate.

Since 1959 the imperial units have been defined in terms of the metre rather than the other way round: an inch is exactly 25.4 millimetres and everything else follows from it. The nautical mile is the interesting one — 1,852 metres exactly, chosen because it is very close to one minute of latitude, which is what makes it useful at sea and useless anywhere else. The survey foot, very slightly different and used in older US land records, was officially retired at the end of 2022 and is not included here.