Kilometres to miles
A kilometre is 0.6213712 miles. The exact number runs the other way: the international mile is defined as exactly 1,609.344 metres, so the kilometres-to-miles factor is that figure’s reciprocal, which does not terminate and is shown here rounded. A 5K is 3.107 miles, a 10K is 6.214, a half marathon is 13.109 and a marathon is 26.219.
How to convert kilometres to miles
Consecutive Fibonacci numbers make a surprisingly good conversion table. Three and five, five and eight, eight and thirteen, thirteen and twenty-one: in each pair the smaller number is roughly the miles and the larger is roughly the kilometres. It works because the ratio between consecutive Fibonacci numbers converges on 1.618 and the mile-to-kilometre factor is 1.609. The gap at that limit is 0.54 per cent, or about 114 metres across a half marathon. The early pairs straddle the limit rather than creeping up on it, so the one you would actually reach for, 13 miles for 21 km, is closer than the limit at 79 metres, while 5 for 8 misses by 123 in the other direction.
Pace is the conversion runners actually need, and it uses the same factor applied to minutes rather than to distance. Multiply a pace in minutes per kilometre by 1.609344 to get minutes per mile: five minutes a kilometre is 8.05 minutes a mile, which reads as 8:03. Speed runs the other way, so 12 km/h is 7.46 mph. A treadmill quietly set to the other unit is how an easy run turns into a hard one.
One thing worth knowing before you blame your watch. Certified road courses are measured along the shortest legal route with a calibrated bicycle, and the measurement includes a deliberate margin of one part in a thousand so that a course can never come out short. That adds about 42 metres to a marathon before anyone runs it. A GPS trace then wanders a little at every corner and under every bridge, so a watch reading 42.4 km at the finish is behaving normally.
What people use it for
- Reading a race distance in miles before entering
- Logging a training run recorded in kilometres
- Converting a training pace between the two units
- Reading a European road sign or route length in miles
- Comparing two watches set to different units
Questions
3.10686 miles, usually quoted as 3.1. A 10K is 6.21371 miles and a half marathon, at 21.0975 km, is 13.1094.
42.195 km is 26.2188 miles. The odd distance was set at the 1908 London Olympics and standardised in 1921.
Multiply minutes per kilometre by 1.609344. A 4:30/km pace is 7.242 minutes a mile, which is a shade under 7:15. Going the other way, divide.
Yes. Both use the international mile of 1,609.344 metres, fixed in 1959. The US survey mile ran about two parts per million longer and was retired at the end of 2022.
A nautical mile is exactly 1,852 metres, which is about 1.151 statute miles. It was set to approximate one minute of latitude. Aviation and shipping use it; road signs never do.
Because the course was measured along the racing line and your watch measured where you actually ran, plus GPS drift. A one per cent overread across a marathon is 420 metres and is entirely ordinary.
Yes. Kilometres per hour and miles per hour share the factor exactly, because only the distance unit changes. Twelve km/h is 7.456 mph.
Almost everywhere signs distances in kilometres. The United Kingdom and the United States are the notable exceptions on road signs, and aviation uses feet and nautical miles regardless of the country underneath.