Speed Converter
Convert between kilometres per hour, miles per hour, metres per second, knots and Mach.
Written by Rahman · Last reviewed
Quick answer
Speed conversion runs through metres per second. One kilometre per hour is 0.2778 m/s, one mile per hour is 0.44704 m/s, and one knot (a nautical mile per hour) is 0.5144 m/s. To go from km/h to mph multiply by 0.6214; the reverse is 1.609.
| Metre per second (m/s) | 1 |
| Kilometre per hour (km/h) | 3.6 |
| Mile per hour (mph) | 2.236936292 |
| Foot per second (ft/s) | 3.280839895 |
| Knot (kn) | 1.943844493 |
| Mach (at sea level) (Ma) | 0.002938669958 |
Common conversions
| 1 km/h | 0.621 mph |
| 2 km/h | 1.243 mph |
| 5 km/h | 3.107 mph |
| 10 km/h | 6.214 mph |
| 25 km/h | 15.53 mph |
| 50 km/h | 31.07 mph |
| 100 km/h | 62.14 mph |
| 1 m/s | 3.6 km/h |
| 2 m/s | 7.2 km/h |
| 5 m/s | 18 km/h |
| 10 m/s | 36 km/h |
| 25 m/s | 90 km/h |
| 50 m/s | 180 km/h |
| 100 m/s | 360 km/h |
| 1 kn | 1.151 mph |
| 2 kn | 2.302 mph |
| 5 kn | 5.754 mph |
| 10 kn | 11.51 mph |
| 25 kn | 28.77 mph |
| 50 kn | 57.54 mph |
| 100 kn | 115.1 mph |
Popular conversions
About the Speed Converter
Speed measures how quickly something moves: the distance covered per unit of time. Common units include kilometres per hour, miles per hour, metres per second, knots and Mach.
This converter is used for travel, sport, weather, aviation and shipping, where speed is reported in different units worldwide.
Knots, and why aviation and shipping use them
A knot is one nautical mile per hour, and because a nautical mile is defined from the Earth's geometry rather than from a land measure, it is not a close cousin of the mile per hour. One knot is about 1.151 mph, or 1.852 km/h exactly.
The convenience is navigational: since one nautical mile equals one minute of latitude, a vessel making 60 knots covers one degree of latitude an hour. That relationship is why the unit persists in marine and aviation use long after most other traditional units were retired.
- Wind speeds in marine and aviation forecasts are almost always in knots, while land forecasts use mph or km/h.
- Treating a knot as a mph figure understates the speed by about 15%.
- Aircraft airspeed is further split into indicated, true and ground speed, which differ with altitude and wind, and a single conversion cannot reconcile them.
Mach is a ratio, not a fixed speed
Mach number is not a unit of speed in the way the others on this page are. It expresses speed as a proportion of the local speed of sound, and the speed of sound varies with the temperature of the air the object is moving through.
This converter uses the sea-level standard value of 340.29 m/s, which is about 761 mph or 1,225 km/h. In the cold air at cruising altitude the speed of sound falls substantially, so the same Mach number corresponds to a noticeably lower true airspeed than the sea-level figure implies.
- Temperature, not altitude or pressure directly, is what changes the speed of sound.
- Any single Mach-to-mph conversion is therefore an approximation tied to a stated atmospheric condition.
- For everyday comparisons the sea-level figure is the standard reference and the one quoted in most sources.
Frequently Asked Questions
How do I convert km/h to mph?
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Multiply kilometres per hour by 0.621371. For example, 100 km/h is about 62.1 mph.
What is a knot?
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A knot is one nautical mile per hour, about 1.852 km/h. It is used in sailing and aviation.
What is Mach 1?
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Mach 1 is the speed of sound, roughly 1,225 km/h (340 m/s) at sea level, though it varies with air temperature.