Length can't be negative
Length can't be negative
Length can't be negative
Length can't be negative
Length can't be negative
Length can't be negative
Length can't be negative
Length can't be negative
Length can't be negative
Type a value into any one of the nine fields and the rest update instantly — there's no separate "convert" step, and no field is more important than another. The metric system is used in almost every country for everyday and scientific measurement; the imperial system remains in daily use in the United States and partially in the United Kingdom.
Metric length units — millimetres, centimetres, metres, kilometres — scale by powers of ten from the metre, the SI base unit. Imperial units — inches, feet, yards, miles — evolved from historical body and land measurements and are still used for everyday distances, road signs and heights in the US and, informally, the UK. Nautical miles are used internationally in aviation and maritime navigation; one nautical mile is defined as one minute of arc along a meridian of the Earth, which makes it directly useful for chart-based navigation in a way metric or imperial units aren't.
This calculator uses metres as the common reference point and converts to and from it, regardless of which field you actually type into: 1 mm = 0.001 m, 1 cm = 0.01 m, 1 km = 1,000 m, 1 in = 0.0254 m, 1 ft = 0.3048 m, 1 yd = 0.9144 m, 1 mi = 1,609.344 m, and 1 nautical mile = 1,852 m exactly.
A physical length or distance is always zero or positive — there's no such thing as −5 metres of anything. If you enter a negative value, this calculator flags it as invalid rather than propagating a meaningless negative figure across every other unit.