Kilometers per Hour to Miles per Hour

Kilometers per hour and miles per hour

A kilometer per hour is 1,000 meters per 3,600 seconds: exactly 1/3.6 m/s. Speed limits, car speedometers and weather reports use km/h in most countries.

A mile per hour is one international mile per hour: exactly 0.44704 m/s, or 1.609344 km/h. Speed limits and speedometers in the US and UK, and pitch speeds in baseball, use mph.

Worked example

Convert 100 km/h: 100 × 0.6213711922 = 62.13711922, so 100 kilometers per hour is 62.13711922 miles per hour. Likewise 200 km/h = 124.2742384 mph.

Estimating in your head

Divide by 1.6 for a quick figure; it is off by about 0.6%. For 100 km/h that gives 62.5 mph, against 62.1371 exactly.

Going the other way

To convert miles per hour to kilometers per hour, divide by 0.6213711922 (or multiply by 1.609344). The swap button between the boxes opens that page.

mph = km/h × 0.6213711922

1 km/h = ≈ 0.2777777778 m/s and 1 mph = 0.44704 m/s, both by definition, so the factor is their ratio: 0.6213711922 (rounded here; the page uses the full value). Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.