Length Converter

Pick the unit you have and the unit you want; the value passes through metres and back out. Every factor is an exact definition rather than a measurement: an inch is 25.4 mm, a foot 0.3048 m, a mile 1609.344 m and a nautical mile 1852 m.

Nine units could be paired 72 ways, and a table of 72 rates would be 72 chances to disagree with itself. This converter keeps one number per unit instead — how many metres it is worth — and routes every conversion through the metre: multiply by the factor of the unit you have, divide by the factor of the unit you want. Adding a unit costs one entry, not seventy-two, and no pair can drift out of step with another. What makes that safe here is that the factors are decisions rather than measurements. The 1959 yard-and-pound agreement fixed the inch at exactly 25.4 mm, and the foot at 0.3048 m, the yard at 0.9144 m and the mile at 1609.344 m follow from it exactly; the nautical mile is defined as exactly 1852 m. Nothing was weighed or paced out, so nothing can shift, and the result is only as imprecise as the six decimal places on screen: 1 m shows as 3.280839895 ft, and the true value simply carries on beyond them. Two distinctions are worth holding on to. Here mi is the land mile of 1609.344 m, while a nautical mile is 1852 m — about 15 % longer — so swapping them silently rewrites a distance. And ft and yd are the international definitions of 1959, not the US survey foot: 2.5 yd is 228.6 cm here, where the survey foot would give 228.600457 cm.