Length Converter

Convert between metres, feet, inches, miles, and other length units, with the exact ratios behind each conversion explained.

How Length Units Actually Relate to Each Other

Length is the oldest measurement humans standardized, and the reason converting between systems still trips people up is that metric and imperial units were built on completely different logic. The metre was originally defined as one ten-millionth of the distance from the equator to the North Pole, giving the metric system a clean base-ten structure where a kilometre is exactly a thousand metres and a centimetre is exactly a hundredth of one. Imperial length units, by contrast, grew out of practical human references — a foot approximating the length of an actual foot, a yard approximating a stride — and were only later standardized to fixed ratios, which is why converting between them involves less tidy numbers, such as one inch equaling exactly 2.54 centimetres, a figure fixed by international agreement in 1959. Once that single reference point is known, every other length conversion follows from it: a foot is twelve inches, so it equals 30.48 centimetres, and a mile, at 5,280 feet, works out to just over 1.609 kilometres. Nautical miles add a third layer entirely, since a nautical mile was defined from the Earth’s circumference rather than either the metre or the foot, which is why it doesn’t convert to either system with a clean ratio.