Length & Distance Converter
Every factor here is exact by international agreement, not rounded. One inch is defined as exactly 25.4 millimetres, and every imperial length follows from that single definition.
Value to Convert
Pick any two units — the full table updates underneath.
All units
The same quantity expressed every other way.
Why the inch is exactly 25.4 millimetres
Until 1959 the inch meant slightly different things in different countries — the US and the UK had drifted apart by about two parts per million, which sounds trivial until you are machining aircraft parts. The International Yard and Pound Agreement fixed the yard at exactly 0.9144 metres, which makes the inch exactly 25.4 millimetres and the foot exactly 0.3048 metres. Those are definitions, not measurements, so they never need rounding.
The one exception: the US survey foot
American land surveying kept the pre-1959 foot, where one foot is 1200/3937 metres — about two parts per million longer. Over a single room the difference is invisible. Across a state plane coordinate system it amounts to several metres, which is why surveyors and GIS professionals still have to state which foot they mean. The US survey foot was officially deprecated at the end of 2022, but historic plats and datasets still use it.
Nautical miles are not just bigger miles
A nautical mile is exactly 1852 metres by international definition, chosen because it approximates one minute of latitude along a meridian. That link to the Earth's geometry is why aviation and marine navigation use it: one nautical mile of northward travel changes your latitude by almost exactly one minute, which makes chart work far simpler than converting statute miles.
Precision and significant figures
Results are shown to a sensible number of significant figures rather than padded with false precision. Converting a measurement that was only accurate to the nearest metre into fourteen decimal places of feet does not make it more accurate — it just hides how rough the original number was.