Kilometres to miles

The formula

miles = kilometres × 0.6213711922

The exactness runs the other way: a mile is defined as exactly 1609.344 metres, so kilometres to miles means dividing by 1.609344, which does not terminate. The factor above is that quotient rounded.

To go the other way, multiply by 1.609344. See miles to km.

Quick reference

Running distances

Race distances are defined in metres and converted into miles rather than the reverse, which is why the imperial figures are never round:

The marathon’s “26 miles 385 yards” is the original — the distance was fixed in imperial at the 1908 London Olympics and only later expressed as 42.195 km.

Speed limits

For speeds rather than distances, see km/h to mph — the factor is the same, but the reference points are different.

The Fibonacci trick

Consecutive Fibonacci numbers approach a ratio of 1.618, and a mile is 1.609 kilometres. The two are close enough that the sequence converts distances in your head:

Take the number of kilometres, find it in the sequence, and read off the one before it. From 8 km onward the error is under 1%. It works for non-Fibonacci numbers by decomposing them: 100 km is 89 + 8 + 3, giving 55 + 5 + 2 = 62 miles against a true 62.14.

Estimating in your head

If the Fibonacci route is too much, take off a third and add back a little: 100 km minus a third is 67, which is high, and 0.6 × 100 is 60, which is low. The truth is 62.