A US speed limit in metric
- Input
- 70 mph to km/h.
- Working
- 70 × 1.609344 = 112.65408 km/h. In metres per second: 112.65408 ÷ 3.6 = 31.29 m/s.
- Result
- 70 mph = 112.65 km/h
Speed Converter
Convert miles per hour, kilometres per hour, knots and metres per second with exact factors and reference speeds, in your browser. Runs entirely in your browser — your numbers never leave this device.
Kilometres per hour → Miles per hour
62.137119 mph
100 km/h = 62.137119 mph
| Unit | Value |
|---|---|
| Metres per second (m/s) | 27.777778 m/s |
| Kilometres per hour (km/h) | 100 km/h |
| Miles per hour (mph) | 62.137119 mph |
| Knots (kn) | 53.99568 kn |
| Feet per second (ft/s) | 91.134442 ft/s |
How it works
km/h = value × factor of the source unit (mph = 1.609344, knot = 1.852, m/s = 3.6); then divide by the target unit's factor
| Reference speed | km/h | mph | m/s | Knots |
|---|---|---|---|---|
| Brisk walking | 5 | 3.11 | 1.39 | 2.70 |
| City driving | 50 | 31.07 | 13.89 | 27.00 |
| 100 km/h cruising | 100 | 62.14 | 27.78 | 54.00 |
| Highway driving | 120 | 74.56 | 33.33 | 64.79 |
| Speed of sound (air, approx.) | 1,234.8 | 767.27 | 343 | 666.74 |
Speed units are length-per-time, so their factors come straight from the length definitions: 1 mph = 1.609344 km/h exactly (the mile in kilometres), 1 knot = 1.852 km/h exactly (one nautical mile per hour), and 1 m/s = 3.6 km/h exactly, because there are 3,600 seconds in an hour and 1,000 metres in a kilometre. Going through km/h connects any pair without a separate factor for each combination.
The knot deserves its definition, since it is the unit most often converted by guesswork. A nautical mile is defined as exactly 1,852 metres and was chosen to match one minute of latitude, which is why ships and aircraft still use it. A speed of 20 knots is therefore 20 × 1.852 = 37.04 km/h — knots are not miles per hour, and treating them as equal understates the speed.
For driving, the conversions that matter are the limit pairs: 30 mph = 48.28 km/h, 50 mph = 80.47 km/h, and 70 mph = 112.65 km/h. The reference table works the other way as well, anchoring unfamiliar units to familiar motion — walking pace, city traffic, highway cruising and the speed of sound.
Worked examples
Kilometres per hour to miles per hour
- Input
- 100 km/h to mph.
- Working
- 100 ÷ 1.609344 = 62.1371.
- Result
- 100 km/h = 62.14 mph
Knots to kilometres per hour
- Input
- 20 knots to km/h.
- Working
- 20 × 1.852 = 37.04.
- Result
- 20 knots = 37.04 km/h
Frequently asked questions
How do I convert mph to km/h quickly?
Multiply by 1.609344 exactly, or by 1.6 for a mental estimate that is within about 0.6%. So 60 mph is exactly 96.56 km/h, and the shortcut gives 96 km/h. Use the exact factor for anything written down, such as a converted speed limit or a vehicle specification.
Is a knot the same as a mile per hour?
No. A knot is one nautical mile per hour, and a nautical mile (1,852 m) is longer than a land mile (1,609.344 m). One knot = 1.852 km/h, while 1 mph = 1.609344 km/h, so a knot is about 15% faster than a mile per hour at the same number.
How do I convert metres per second to km/h?
Multiply by 3.6. A wind or projectile speed of 30 m/s is 30 × 3.6 = 108 km/h, which is 108 ÷ 1.609344 = 67.11 mph. The reverse — km/h to m/s — divides by 3.6, which is why a 100 km/h car is moving at 27.78 m/s.
What speed is the speed of sound in mph?
The speed of sound in air at around 20 °C is approximately 343 m/s. That is 343 × 3.6 = 1,234.8 km/h, and 1,234.8 ÷ 1.609344 = 767.27 mph. It varies with temperature and altitude, so treat it as an approximate reference, unlike the exact unit factors on this page.
Why do aircraft and ships use knots instead of mph?
Because the nautical mile ties directly to latitude: one nautical mile is one minute of arc on the Earth's surface, which makes chart work simpler. The knot (one nautical mile per hour) follows from that, and the factor is exact — 1 knot = 1.852 km/h by definition.
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