Length Converter
How it works
Eight units in both directions would be 56 separate formulas, so the converter does not write any of them out. Every length is turned into metres first — multiplying by the entered unit's factor — and then divided back out by each of the eight units' own factor. One factor per unit, and the eight answers cannot disagree with each other.
Those factors are definitions rather than rounded measurements: 1 in = 0.0254 m and 1 mi = 1609.344 m exactly, by international agreement, and every metric unit is exact by construction of its prefix — a kilometre is 1000 m because "kilo" means 1000, not because someone measured it. So nothing here loses precision beyond ordinary floating-point division.
Unlike the temperature converter, there is no floor enforced on the value: a length has no equivalent of absolute zero, so a negative number is accepted and converted as a signed relative measurement rather than rejected.
Frequently asked questions
Why show all 8 units at once?
Because the second unit you need usually follows the first. Someone converting a plank length from centimetres to inches often wants the feet next to it, and someone converting a race distance from kilometres wants the miles — showing the whole row means you never change the target unit and read the page twice.
How precise are these conversions?
Exact, not rounded approximations. A mile is defined as exactly 1609.344 metres, an inch as exactly 0.0254 metres, and every metric unit is exact by construction of its prefix — so the only imprecision anywhere here is ordinary floating-point division, not a rounded conversion factor.
Does it handle negative lengths?
Yes. A negative value is treated as a signed relative measurement — a displacement or a difference — rather than rejected, since unlike a temperature there is no physical floor a length cannot go below.