What it does
This converter changes a distance between miles and kilometres, in either direction. Type a number and the answer appears as you type; the swap button flips which unit you are converting from. Nothing is sent to a server — the arithmetic runs in your browser.
How it works
There is one number to remember: 1 mile is exactly 1.609344 kilometres. That is a definition, not a measurement. Under the 1959 international yard and pound agreement, the international mile was fixed at exactly 1,609.344 metres — so the conversion is exact and never rounds at source.
To go from miles to kilometres you multiply by 1.609344; to go the other way you divide by 1.609344. The two operations undo each other, so converting a value and then converting it back returns the number you started with (bar any display rounding).
Worked example
Take 10 miles. Multiplying by the factor gives 10 × 1.609344 = 16.09344, so 10 miles is 16.09344 km. A 10-mile ride is a useful anchor: it is a shade under 16.1 km, so a 10-mile stretch of British motorway corresponds to about the same distance you would see signed as 16 km on the Continent.
Common uses
- UK road distances: British road signs and speedometers are in miles. Turning a mileage into kilometres is handy for planning trips into Europe, where signs and satnavs read in km.
- Running and marathons: a marathon is 26.2 miles, or 42.195 km — race listings and training plans mix the two, so runners routinely convert splits and pace.
- Cars and road trips: hire-car odometers, fuel economy figures and continental crossings often flip between the units on the same journey.
- Visiting the US: American distances, speed limits and directions are in miles, so UK visitors used to kilometres from European travel benefit from a quick conversion.
Frequently asked
Is a mile always 1,609.344 metres?
The mile used today is: this is the international mile, defined as exactly 1,609.344 metres since 1959. Older definitions — the statute mile, the survey mile, various historic country miles — differed slightly, but for road, running, aviation and everyday use the international mile is what "mile" means. The US survey mile (about 3.2 mm longer than the international mile) was built on the US survey foot; NIST and the National Geodetic Survey retired the US survey foot on 1 January 2023, so all official US federal work now uses the international foot — and, by extension, the international mile.
What's the shortcut for rough conversions?
Multiply miles by 1.6 for a quick estimate — 30 miles is roughly 48 km. For a slightly better mental sum, use × 8 ÷ 5: 30 × 8 = 240, then ÷ 5 = 48. Going the other way, kilometres × 5 ÷ 8 gets you close, or divide by 1.6. These shortcuts are within about half a percent of the exact factor — fine for planning, but for anything precise use the converter above.
How many kilometres is a marathon?
26.2 miles works out to about 42.16 km using the rounded race distance. The formally defined marathon is 42.195 km (26 miles 385 yards), so the "26.2" figure is itself a rounding of the true race length.
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