Length conversion through exact factors
This converter translates between the eight length units of everyday life — millimetres, centimetres, metres and kilometres, and inches, feet, yards and miles — and shows your length in all of them at once, because conversion questions rarely stop at one pair. Every value is computed through metres using the exact international definitions: since 1959 the inch has been defined as exactly 25.4 millimetres, which makes the foot exactly 0.3048 m and the mile exactly 1609.344 m. There is no rounding anywhere in the chain except in the final display.
The factor method
Converting through a base unit keeps all 56 possible unit pairs consistent with just eight factors — direct pair tables can disagree with each other after rounding, a base-unit chain cannot. The step panel shows both multiplications for your numbers. Mental landmarks worth keeping: a metre is about 3.28 feet; a kilometre is 0.6214 of a mile (so multiply miles by 1.609 for km); an inch is 2.54 cm; and a yard is 0.9144 m — slightly less than a metre, which is the source of many near-miss estimates.
Feet and inches, the awkward pair
Imperial heights and room sizes come as mixed units — 5 ft 9 in — which are not decimal. The stats panel on this page always shows your length in feet-and-inches form alongside the others. To convert a mixed value, convert the feet and inches separately and add: 5 ft = 152.4 cm and 9 in = 22.86 cm, so 5 ft 9 in = 175.26 cm. The construction calculators in this site's Construction section take feet and inches natively for areas.
Worked example
1 mile is exactly 1.609344 kilometres — and the same table tells you it is also 5,280 feet, 1,760 yards and 1,609,344 millimetres.
How to use this calculator
- Enter the length.
- Choose the unit it is in and the unit you want.
- Read the headline answer, then scan the all-units table for every other unit.
- Use the step panel if you need the working for homework or a report.
Why the mile is 1,609.344 metres exactly
The statute mile was fixed at 5,280 feet in Elizabethan England (chosen so a furlong of 660 feet divided it neatly by 8). When the English-speaking world agreed in 1959 to define the inch as exactly 25.4 mm, the mile inherited exactness: 5,280 × 12 × 25.4 mm = 1,609.344 m to the last digit. The nautical mile is a different creature entirely — 1,852 m, defined by Earth's geometry — and is not used on this page.
Converting one specific pair? These single-pair pages are pre-set and carry a full table for that pair: Cm to Inches, Inches to Cm, Mm to Inches, Inches to Mm, Miles to Km, Km to Miles, Feet to Meters and Meters to Feet — plus areas on Square Feet to Square Meters and Square Meters to Square Feet. For volume there is no combined converter here — use the dedicated Liters to Gallons and Gallons to Liters pages.