What is a 50 km/h city limit in mph?

50 km/h is 31.068560 mph, which is why British and American towns tend to post 30 mph — the two limits are close enough to feel identical behind the wheel.

Is 100 km/h the same as 60 mph?

Not quite. 100 km/h is 62.137119 mph, so a car cruising at an indicated 60 mph is doing about 96.6 km/h. The gap is small but it is the difference between keeping up with traffic and holding it up.

Why do ships and aircraft use knots?

A knot is one nautical mile per hour, and a nautical mile is 1852 meters — roughly one minute of latitude. That makes navigation arithmetic on a chart far simpler than it would be with statute miles.

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km/h to mph

Convert kilometers per hour to miles per hour. The ratio is the same exact 1.609344 that relates the two distance units, because an hour is an hour on both sides.

mph = km/h ÷ 1.609344

NIST SP 811 (2008), Appendix B.8 — mile per hour (mi / h) to kilometer per hour (km / h) = 1.609 344 E+00

Speed conversion inherits its factor from distance: the hour cancels out, so kilometers per hour to miles per hour uses exactly the same 1.609344 that converts the distances themselves. This is the conversion drivers need when a rental car shows the wrong unit, and the one sailors avoid entirely by using knots, which are nautical miles per hour rather than statute ones.

How it is calculated

mph = km/h ÷ 1.609344

Because both scales measure distance over the same unit of time, the time cancels and only the distance factor remains. NIST publishes the same number for the speeds as for the lengths.

Source: NIST SP 811 (2008), Appendix B.8 — mile per hour (mi / h) to kilometer per hour (km / h) = 1.609 344 E+00

Common values

kilometers per hour	miles per hour
10	6.2137119
30	18.641136
50	31.06856
60	37.282272
80	49.709695
90	55.923407
100	62.137119
110	68.350831
120	74.564543
130	80.778255
140	86.991967

Questions people ask

What is a 50 km/h city limit in mph?: 50 km/h is 31.068560 mph, which is why British and American towns tend to post 30 mph — the two limits are close enough to feel identical behind the wheel.
Is 100 km/h the same as 60 mph?: Not quite. 100 km/h is 62.137119 mph, so a car cruising at an indicated 60 mph is doing about 96.6 km/h. The gap is small but it is the difference between keeping up with traffic and holding it up.
Why do ships and aircraft use knots?: A knot is one nautical mile per hour, and a nautical mile is 1852 meters — roughly one minute of latitude. That makes navigation arithmetic on a chart far simpler than it would be with statute miles.

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