Precision unit conversion
Length is the most-converted category on this site — mostly people going between metric measurements (mm, cm, m, km) and imperial ones (inches, feet, yards, miles) for DIY, travel and everyday jobs. Here's how the units relate, with a quick reference table and the formulas behind each conversion.
The metric system is built on the metre and scales by powers of ten: 10 millimetres make a centimetre, 100 centimetres make a metre, and 1,000 metres make a kilometre. The imperial system used in the UK and US doesn't scale as neatly — 12 inches make a foot, 3 feet make a yard, and 1,760 yards make a mile — which is exactly why a converter is more useful here than mental maths.
| Convert | Result |
|---|---|
| 1 inch | 25.4 mm |
| 1 foot | 30.48 cm (0.3048 m) |
| 1 yard | 0.9144 m |
| 1 mile | 1.60934 km |
| 1 metre | 39.3701 in (3.28084 ft) |
| 1 kilometre | 0.62137 mi |
| 1 cm | 0.393701 in |
mm → in: divide by 25.4. In → mm: multiply by 25.4. Feet → metres: multiply by 0.3048. Metres → feet: divide by 0.3048. Miles → km: multiply by 1.60934. Km → miles: divide by 1.60934 (or multiply by 0.62137).
The converter also accepts fractions and mixed numbers directly, so you can type something like 43 3/4 for a joiner's or plumber's measurement in inches and get an exact millimetre reading, rather than converting the fraction to a decimal yourself first.
The full tool converts between all eight length units at once, remembers your last-used units, and supports fractional inch input for trade and DIY measurements.
Open Length converter →There are exactly 25.4 millimetres in one inch. This is the internationally agreed definition, so it's an exact conversion rather than a rounded approximation.
Multiply the number of feet by 0.3048. For example, 6 feet is 1.8288 metres.
There are 5,280 feet in a mile (1,760 yards × 3 feet).
Yes — the statute mile (1,609.344 metres) is the same length in both the UK and US. Nautical miles, used at sea and in aviation, are different again at 1,852 metres.
Enter it directly into the converter as "43 3/4" — it parses mixed numbers and simple fractions automatically, so 43 3/4 inches converts to about 1,111.25 mm without you needing to do the fraction maths first.