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Speed conversions hang on one clean metric anchor - 1 m/s is 3.6 km/h - and one imperial one: 1 mph is 0.44704 m/s, which is 1.609344 km/h. Everything else follows. A 60 mph limit is 96.6 km/h, and a 100 km/h limit is 62 mph.
Knots are nautical miles per hour by definition rather than by coincidence, which is why they belong at sea. One knot is 1.852 km/h, and because one minute of latitude is one nautical mile, a speed in knots maps straight onto a chart. The approximation to avoid is 1.5: it puts 60 mph at 90 km/h instead of 96.6, an error of 7%.
| m/s | km/h | mph | kn | ft/s | |
|---|---|---|---|---|---|
| 1 m/s | 1 | 3.6 | 2.236936 | 1.943846 | 3.28084 |
| 1 km/h | 0.277778 | 1 | 0.621371 | 0.539957 | 0.911344 |
| 1 mph | 0.44704 | 1.609344 | 1 | 0.868977 | 1.466667 |
| 1 kn | 0.514444 | 1.851998 | 1.150778 | 1 | 1.687808 |
| 1 ft/s | 0.3048 | 1.09728 | 0.681818 | 0.592484 | 1 |
How do I convert km/h to mph? Multiply by 0.621371, or divide by 1.609344. A 100 km/h limit is 62.1 mph. The rough factor of 0.6 gets you close, but it drifts as the numbers grow.
What is a knot in km/h? 1.852 km/h exactly, since one nautical mile is 1,852 m. So 20 knots is 37 km/h, and a 30-knot boat is making about 55 km/h.
How fast is 1 m/s in km/h? 3.6 km/h, and this is exact - it comes from 3,600 seconds in an hour divided by 1,000 meters in a kilometer. It is the cleanest anchor in the category.
Is mph the same as km/h? No. Miles per hour is the imperial measure used in the US and the UK, and kilometers per hour is the metric one used almost everywhere else. One mph is 1.609 km/h, so a 70 mph motorway speed is 113 km/h.
How do I convert mph to m/s? Multiply by 0.44704, since one mile is 1,609.344 m and one hour is 3,600 seconds. So 60 mph is 26.8 m/s. Use this conversion whenever a physics or engineering formula expects SI units.