How it works
Why the UK still straddles two systems
The United Kingdom legally adopted the metric system decades ago, but daily life is stubbornly bi-metric. Road distances, car speedometers and personal height are still quoted in miles, mph and feet-inches; maps, construction drawings and school physics run on metres and kilometres. This length converter handles both sides cleanly so you never have to memorise the constants.
Everything on this page uses the internationally-agreed exact factors published by the UK National Physical Laboratory and enshrined in the 1959 international yard and pound agreement.
The exact conversion factors you actually need
These are the only numbers you ever need to remember — every other length conversion is built from them.
- 1 inch = 2.54 cm (defined exactly)
- 1 foot = 12 inches = 30.48 cm = 0.3048 m
- 1 yard = 3 feet = 0.9144 m
- 1 mile = 1,760 yards = 1,609.344 m = 1.609344 km
- 1 nautical mile = 1,852 m (used in aviation and at sea, not on UK roads)
- 1 metre = 39.3701 inches ≈ 3.281 feet
- 1 km = 0.621371 miles
Three real UK conversions, worked
Below are the three length conversions we get asked about most often.
Height in feet & inches to centimetres
A six-foot-tall adult is exactly 6 × 30.48 = 182.88 cm. To add inches, multiply by 2.54: 5 ft 10 in = (5 × 30.48) + (10 × 2.54) = 152.4 + 25.4 = 177.8 cm. UK medical records and many fitness apps store height in centimetres, so this is the conversion you'll need when you switch between apps.
Motorway distance miles to kilometres
Manchester to London is roughly 200 miles on the motorway. In kilometres that's 200 × 1.609344 ≈ 321.9 km. When your satnav switches units (or you're driving in France) the reverse is handy: 450 km ≈ 450 × 0.621371 ≈ 279.6 miles.
DIY: metres to inches for picture hanging
Flat-pack furniture ships with metric measurements, but many UK stud-finders and plasterboard specs still quote inches. A 1.2 m shelf = 1.2 × 39.3701 ≈ 47.24 inches — or almost exactly 4 feet. Useful when you're checking whether a new bookcase will fit into a 4-foot alcove.
Common mistakes to avoid
- Mixing UK and US units. A UK nautical mile and a US nautical mile are identical, but a UK gallon is not a US gallon — be aware which country a source is from.
- Forgetting that a hand (horse height) is 4 inches, and a chain (cricket pitch) is 22 yards = 20.1168 m. Niche, but they come up in land surveying and sport.
- Rounding 2.54 to 2.5 — a 1.5% error that compounds when you're converting floor plans.
- Assuming running pace in min/mile and min/km are interchangeable with a simple factor. They need dividing, not multiplying: 8 min/mile ≈ 4.97 min/km, not 8 × 1.609.
- Reading "m" as metres when a maritime chart means nautical miles. Check the legend.
Works well with
Length conversions almost never happen in isolation — you're usually sizing something up. These companion calculadoras are the ones we reach for next:
- **Area of a rectangle** — once you've got dimensions in the same unit.
- **Area of a circle** — for round tables, flower beds or lids.
- **Weight converter** — kilograms to stones and pounds.
- **Speed converter** — miles per hour to kilometres per hour.
How we keep this accurate
Length conversion factors are exact by definition — there is nothing to round. The calculadora uses double-precision arithmetic and only rounds for display, preserving accuracy for engineering and construction work. Read our editorial policy and corrections policy to see our full sourcing and review process.