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Speed Converter
Speed Converter
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How speed conversion works
Speed is distance divided by time, so every speed conversion is a length conversion with the time unit carried along. Converting metres per second to kilometres per hour multiplies by 3.6 because there are 3,600 seconds in an hour and 1,000 metres in a kilometre, and 3600/1000 is 3.6.
The knot is the odd one out: it is one nautical mile per hour, and a nautical mile is a minute of latitude rather than a land measure. That is why aviation and shipping quote speeds in knots and altitudes in feet while using metric for almost everything else.
Formulas
Metres per second to km/h
km/h = m/s × 3.6
Miles per hour to km/h
km/h = mph × 1.609344
Knots to km/h
km/h = kn × 1.852
Exact: a nautical mile is 1,852 m by definition.
Worked examples
| From | To | Result |
|---|---|---|
| 1 m/s | km/h | 3.6 km/h |
| 100 km/h | mph | 62.1371 mph |
| 60 mph | km/h | 96.5606 km/h |
| 1 knots | km/h | 1.852 km/h |
| 30 mph | m/s | 13.4112 m/s |
Results are computed with the same factors the converter above uses, rounded to six significant figures.
Common speeds
| km/h | mph | m/s |
|---|---|---|
| 5 | 3.10686 | 1.38889 |
| 30 | 18.6411 | 8.33333 |
| 50 | 31.0686 | 13.8889 |
| 80 | 49.7097 | 22.2222 |
| 100 | 62.1371 | 27.7778 |
| 120 | 74.5645 | 33.3333 |
| 130 | 80.7783 | 36.1111 |
5 km/h is a walking pace. The rest are the speed limits used across most of Europe.
Worth knowing
- 1 mph = 0.44704 m/s exactly, because a mile is exactly 1,609.344 m.
- 1 knot = 1.852 km/h exactly = 1.15078 mph.
- The common highway limits line up closely but not exactly: 100 km/h is 62.14 mph, and 60 mph is 96.56 km/h.
- To estimate mph from km/h in your head, halve it and add 10%: 100 km/h → 50 + 5 = 55, against a true 62. Better is to multiply by 5/8, which gives 62.5.
Frequently asked questions
- How do I convert km/h to mph quickly?
- Multiply by 5 and divide by 8. That gives 62.5 for 100 km/h against a true 62.14, an error under 1%. The exact factor is 0.621371.
- What is a knot and why is it not just mph?
- A knot is one nautical mile per hour, and a nautical mile is one minute of arc of latitude, or 1,852 metres. It survives in navigation because it makes chart work arithmetic: a vessel doing 10 knots covers 10 minutes of latitude an hour. One knot is 1.15 mph.
- Is 60 mph exactly 100 km/h?
- No, though the coincidence is close enough that people treat them as equivalent. 60 mph is 96.56 km/h, and 100 km/h is 62.14 mph. The 4% gap is why a car set to a 100 km/h limiter reads just over 62 on a mph speedometer.
- Why is aviation altitude in feet when everything else is metric?
- Standardisation, not preference. Almost all of the world's civil aviation infrastructure and instrumentation was built around feet, and separating aircraft vertically requires that every aircraft in a region uses the same unit. China, Russia and a few neighbours use metres, which is a known handover hazard.