Miles to km Converter

The exact figure

This follows directly from the 1959 definition of the yard as 0.9144 metres. A statute mile is 1,760 yards, so the mile became exactly 1,609.344 metres as a consequence. Like the other post-1959 factors, it is a definition and carries no uncertainty.

The mile itself descends from the Roman mille passus, a thousand paces of five Roman feet each, which came to roughly 1,480 metres. The modern figure drifted upward over centuries of English usage before being fixed by statute in 1593 at the 1,760 yards it remains.

The race distances people are actually looking up

Running is one of the few places where both systems are used simultaneously, often within the same event. A 5K is 3.107 miles, a 10K is 6.214 miles, a half marathon at 21.0975 km is 13.109 miles, and a marathon at 42.195 km is 26.219 miles.

The marathon distance is oddly specific because it was set at the 1908 London Olympics, where the course ran from Windsor Castle to the royal box at White City Stadium, and the resulting 26 miles and 385 yards was standardised in 1921. So the definitive distance of the world's most famous race is a metric conversion of an arbitrary imperial course length.

Speed limits and the 5-to-8 rule

The neatest mental shortcut here is that 5 miles is almost exactly 8 kilometres — 8.04672 to be precise, an error of about 0.6%. That makes speed limits easy: 30 mph is roughly 48 km/h, 60 mph roughly 96, and 70 mph roughly 112. The real values are 48.28, 96.56 and 112.65, so the shortcut is consistently a shade low but never misleading.

It works the other way too: a 100 km/h limit is about 62 mph, and 130 km/h is about 81 mph. Worth knowing when driving abroad, where the number on the sign is the same but the unit is not, and where a habit of reading 100 as a familiar figure can be expensive.

Nautical miles are a different unit

A nautical mile is 1,852 metres exactly, about 15% longer than a statute mile, and converting marine or aviation distances with the factor above will give you a wrong answer.

The reason for the difference is that a nautical mile was defined geographically: one minute of latitude along a meridian, so that one degree of latitude equals sixty nautical miles. That makes chart work straightforward in a way no land unit can match, since distance can be read directly off the latitude scale. Aircraft and ships still use it, and speed in knots means nautical miles per hour — which is why a knots conversion is its own calculation.

Frequently asked questions