Kilometres to miles
One kilometre is 0.621371 miles, because the international mile is defined as exactly 1,609.344 metres. Multiply kilometres by 0.621371 to get miles. A 5K is 3.11 miles, a 10K is 6.21 miles, a half marathon is 13.11 miles and a marathon is 26.22 miles.
How to convert kilometres to miles
The closest easy approximation is the Fibonacci trick: consecutive Fibonacci numbers are roughly a kilometre-to-mile pair, because the golden ratio, 1.618, is within half a per cent of 1.609. Five kilometres is about three miles, eight is about five, thirteen is about eight. It falls apart above about 100, where the accumulated error is a mile and a half.
Questions
3.10686 miles, usually quoted as 3.1. A 10K is 6.21 miles and a marathon, at 42.195 km, is 26.219 miles.
Yes. Both use the international mile of 1,609.344 metres, fixed in 1959. The US survey mile, about 3 mm longer, was retired for most purposes at the end of 2022.
A nautical mile is 1,852 metres, roughly 1.15 statute miles. Aviation and shipping use it; road signs never do.
Speedometers and trip meters are allowed to over-read by a few per cent and never to under-read, so a dashboard mileage is normally a little higher than the true distance.