Kilometers per Hour to Miles per Hour

Almost every country outside the US and UK signs speeds in km/h, so American and British drivers abroad convert constantly. A 50 km/h town limit is 31 mph, a 30 km/h school or residential zone 18.6 mph, a 100 km/h rural or motorway limit 62 mph, and 120 km/h 74.6 mph. France and Italy allow 130 km/h on motorways in good conditions, which is 80.8 mph, and Germany's recommended speed on unrestricted autobahn sections is also 130 km/h.

Canada switched its road signs to km/h in 1977 and Ireland in 2005, so crossing from Northern Ireland, where limits are in mph, into the Republic means the numbers on the signs jump even though the speeds do not.

Multiplying by 0.6 gives a result about 3.4% low, which is fine for a rough idea. A better shortcut is to halve the km/h figure and add a quarter of that half: 80 km/h becomes 40 + 10 = 50 mph, against the exact 49.7. Most speedometers show both scales: cars sold in the US and UK put mph on the main dial with a smaller km/h ring, while cars sold in Europe do the opposite.

For precise work, such as comparing performance data or wind speeds, use the converter or the full factor.

Multiplying by 1.6 instead of dividing gives a bigger number, which can never be right: a mile is longer than a kilometer, so the mph figure is always smaller. The other slip is in a rental car with only a km/h speedometer, reading 100 on a 62 mph road and assuming you are speeding.

The reverse, with the US and UK limits, is on mph to km/h. For distances rather than speeds, see kilometers to miles.