Miles vs kilometres — the global distance standoff
Why two units of distance have coexisted for centuries, and which one you should expect to see.
1 mile = 1.609 km (US + UK road distances)
1 km = 0.621 miles (everywhere else)
The metric system has been legal for road measurement in the UK since 1897 — but road signs are still in miles (deliberately, by act of Parliament in 1983). The US has debated conversion multiple times and never passed legislation.
| Use | Most common unit | |---|---| | US road sign | mile | | US highway speed limit | mph | | UK road sign | mile | | UK car speedometer | both | | EU road sign | km | | Japan road sign | km | | Running event | km (5K, 10K) or mile (mile fun-run) | | Aviation distance | nautical mile | | Maritime distance | nautical mile | | Astronomy | AU, light-year, parsec |
Conversions: - 1 mile = 1.609344 km exactly - 1 km = 0.621371 miles - 5 miles ≈ 8.04672 km - 100 km ≈ 62.137 miles
Traps: running shoes, treadmills, and swimming pool sizes often use both side-by-side. The site lets you convert any number to any unit with the right precision.
Frequently Asked Questions
Which should I use?
Use miles for US / UK road distances and for running events measured in miles.
When is the alternative better?
Use km for international road distances and most scientific / sporting contexts.
How is the conversion calculated?
Every conversion is a single factor (or an affine formula). The math is identical either direction; the difference is context.