Convert miles to kilometers

The formula

kilometers = miles × 1.609344

miles to kilometers — quick reference

Add half, then add a tenth

Multiplying by 1.6 is easier as two additions: take the mileage, add half of it, then add a tenth of the original. Seventy miles becomes 70 plus 35 plus 7, or 112 km, against a true 112.65. The Fibonacci pairs run backwards too - 3 miles is about 5 km, 5 about 8, 8 about 13.

The shortcut is consistently short, since 1.6 sits 0.6 per cent below the true 1.609344. On a ten-mile run that is invisible; on a 3,000-mile road trip it loses about 28 km. Add one per cent back only if the distance is large enough for the gap to mean anything.

Not every mile on the sign is the statute mile

The statute mile has been exactly 1,609.344 m since the 1959 international yard and pound agreement. The nautical mile is a different unit entirely at 1,852 m, about 15 per cent longer, and it is the one meant whenever the context is a chart, a flight plan or a marine forecast. Distances at sea converted as statute miles come out badly wrong.

Then there is the Scandinavian mil, still in everyday spoken use in Sweden and Norway, which is 10 km. Someone saying a place is two mil away means 20 km, not two miles. British road signs, meanwhile, remain in miles and yards: the 30, 60 and 70 mph limits are 48, 97 and 113 km/h.

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