1 km/h = 0.621372 mph
About speed units
Speed is distance per time. Convert meters per second, kilometers per hour, miles per hour and knots for roads, sports, wind and navigation.
In short
To convert km/h to mph, multiply by 0.621371. One knot equals one nautical mile per hour (exactly 1.852 km/h).
Road speed limits
Most of the world posts limits in km/h; the US uses mph. 100 km/h ≈ 62 mph; 70 mph ≈ 113 km/h. Rental cars and dash displays may not match the country you are driving in—convert the sign, not your gut feel.
Running & cycling pace
Treadmills and bike computers often show mph or km/h while training plans talk pace per kilometer or mile. Convert a steady speed once (for example 10 km/h ≈ 6.2 mph) so pace charts and device screens agree.
Wind reports
Weather services publish wind in km/h, mph or knots depending on the audience. 30 knots ≈ 56 km/h ≈ 35 mph. Sailors and aviation briefings favor knots; local TV weather often uses the national road unit.
Knots at sea and in the air
A knot is one nautical mile per hour. Because charts use nautical miles, pilots and mariners keep speed in knots for dead reckoning. Convert to km/h or mph only when explaining conditions to a general audience.
Physics class (m/s)
Textbooks and lab sensors prefer meters per second. 1 m/s = 3.6 km/h ≈ 2.24 mph. Convert exam answers into the unit the problem statement asks for—mixing m/s with km/h is a classic lost-points mistake.