Length & Distance Converter

Ten units in one grid — micrometre, millimetre, centimetre, metre, kilometre, inch, foot, yard, mile and nautical mile — each recomputed as you type. The imperial side is not approximated: since the international yard and pound agreement of 1959 the inch has been exactly 25.4 mm, which makes the foot exactly 0.3048 m, the yard 0.9144 m and the statute mile 1609.344 m by definition rather than by measurement.

That agreement is also why "foot" was ambiguous in the United States for another sixty years. The older US survey foot was 1200/3937 m, longer than the international foot by exactly 2.000004 parts per million. That sounds like nothing and is nothing over a room, but it is 3.2 mm over a mile and 20 cm over 100 km — enough to move a property corner, which is why land surveys kept the old value. NIST and the National Geodetic Survey retired the survey foot at the start of 2023; this tool uses the international foot throughout, so a coordinate taken from an older state plane grid will not agree with it at the last digit.

The nautical mile is the one unit here that is not a multiple of anything else. It is exactly 1852 m by international agreement, chosen to approximate one minute of arc along a meridian — an arc that is not constant, because the Earth is flattened: on the WGS 84 ellipsoid a meridian arcminute runs 1842.9 m at the equator and 1861.6 m at the pole. The agreed value sits close to the figure at 45° latitude, which works out at 1852.2 m, so the definition is within about 20 cm of the thing it was meant to represent.

Results carry eight significant digits, capped at eight decimal places, and switch to exponential notation below 0.0001 — a micrometre in kilometres reads 1.0000e-9.