Length / Distance Converter

How it works

Length conversions translate measurements between metric (millimeters, centimeters, meters, kilometers) and imperial/US customary (inches, feet, yards, miles) units. Almost every country except the US, Liberia, and Myanmar uses metric exclusively, but the US uses imperial for everyday measurement and metric for science and medicine, so the conversions show up frequently.

Key conversions to memorize: 1 inch = 2.54 cm exactly (this was redefined to be exact in 1959); 1 meter ≈ 3.281 feet; 1 mile = 1.609 km; 1 yard = 0.9144 m exactly. These ratios chain together: a marathon is 26.2 miles ≈ 42.2 km; a meter stick is roughly a yard plus 3 inches.

For everyday estimation, useful approximations: a meter is about a yard (slightly longer); 100 km/h is about 62 mph; a kilometer is roughly 5/8 of a mile; 30 cm is about a foot. Going the other way, 5 feet is roughly 1.5 m, 6 feet is about 1.83 m, and 100 mph is about 161 km/h.

Be careful with units that share names but mean different things. The "nautical mile" used in aviation and maritime navigation is 1.852 km — different from the statute mile of 1.609 km. The "international foot" (1959 definition) is 0.3048 m exactly; older US "survey foot" definitions differ by a few parts per million and are still used for some land surveys.

This calculator uses double-precision floating point and the conversion factors are accurate to better than 1 part in 10¹². For engineering work that requires more precision, use a unit-aware library (Pint in Python, units in MATLAB) that tracks unit dimensions symbolically.