Miles to Kilometers

The word mile comes from the Latin mille passus, a thousand paces, where a pace was a double step of about five Roman feet. That Roman mile was roughly 1,480 m. England kept the name but changed the length: an Act of Parliament in 1593 fixed the statute mile at eight furlongs of 660 feet, which is 5,280 feet, partly so that it divided neatly into the furlongs farmers already used.

The length in meters was settled by the international yard and pound agreement of 1959, which made the yard exactly 0.9144 m and therefore the mile exactly 1,609.344 m. The US kept a slightly longer survey mile for land records until the US survey foot was retired at the end of 2022; the difference is about 3 mm per mile, which only surveyors ever noticed.

American and British speed limits are in miles per hour, so visitors convert them constantly. 30 mph is 48.3 km/h, 55 mph is 88.5 km/h and 70 mph, the UK motorway limit, is 112.7 km/h. Electric car ranges are advertised the same way: a 300-mile EPA range is 482.8 km, although real-world range in winter is usually lower in either unit.

Fuel economy needs more than a single factor, because metric countries turn the ratio upside down and quote liters per 100 km. Divide 235.21 by the miles-per-gallon figure (US gallons) to get liters per 100 km: 30 mpg is 7.84 L/100 km and 40 mpg is 5.88 L/100 km. British mpg figures use the larger imperial gallon, so the same car shows a higher mpg number in the UK.

Add 60% to the miles: 50 mi plus 30 is 80 km, against the exact 80.47 km. For long distances add a little more, since the true factor is 1.609. A 100-mile ultramarathon is 160.93 km and the 26.2-mile marathon is 42.2 km.

Do not use this factor for sea or air routes. Pilots and sailors measure in nautical miles of exactly 1,852 m, about 15% longer than a statute mile. For the reverse trip, from kilometers to miles, use the km to miles page; the unit converter covers feet, yards and nautical miles too.