Convert between km/h, mph, m/s and knots instantly.
This converts between the units used for vehicle speeds, wind, running pace and aviation. Speed is distance divided by time, so every conversion here is a length conversion combined with a time conversion.
The metres-per-second to kilometres-per-hour factor of exactly 3.6 is the one worth memorising, since m/s is the SI unit that appears in every physics calculation while km/h is what the sign by the road says.
| km/h | mph | m/s | knots | Context |
|---|---|---|---|---|
| 5 | 3.1 | 1.4 | 2.7 | Walking |
| 20 | 12.4 | 5.6 | 10.8 | Cycling |
| 50 | 31.1 | 13.9 | 27.0 | Urban speed limit |
| 80 | 49.7 | 22.2 | 43.2 | Rural road |
| 100 | 62.1 | 27.8 | 54.0 | Motorway |
| 120 | 74.6 | 33.3 | 64.8 | Motorway, higher limit |
| 900 | 559 | 250 | 486 | Airliner cruise |
| 1,235 | 767 | 343 | 667 | Speed of sound at sea level |
A knot is one nautical mile per hour, and a nautical mile is one minute of latitude. That relationship is what keeps it in use: a navigator working with a chart marked in degrees of latitude can read distance directly off the scale without any conversion factor. The name comes from the practice of measuring a ship's speed by paying out a knotted line behind it and counting the knots that passed in a fixed interval.
Aviation and marine speeds are quoted in knots almost universally, as is wind speed in weather reporting for both. A useful rule for pilots and sailors: knots are roughly 15% higher than mph, so 100 knots is about 115 mph or 185 km/h.
Runners work in pace — minutes per kilometre or per mile — which is the reciprocal of speed. Faster means a lower number, which inverts the intuition.
A 12 km/h runner is at 5:00 min/km. A 5:30 min/km pace is 10.9 km/h. Converting a pace between miles and kilometres means multiplying or dividing by 1.609: a 8:00 min/mile pace is 4:58 min/km.
| Pace min/km | Speed km/h | Pace min/mile | Marathon time |
|---|---|---|---|
| 4:00 | 15.0 | 6:26 | 2:48:48 |
| 5:00 | 12.0 | 8:03 | 3:30:59 |
| 6:00 | 10.0 | 9:39 | 4:13:11 |
| 7:00 | 8.6 | 11:16 | 4:55:22 |
Mach number is speed relative to the local speed of sound, which is not a constant — it depends on air temperature, falling as air gets colder. At sea level in standard conditions sound travels at about 343 m/s or 1,235 km/h, but at typical airliner cruising altitude, where the air is around -55 C, it drops to roughly 295 m/s or 1,062 km/h. An aircraft at Mach 0.85 is therefore doing about 900 km/h up high, considerably slower in absolute terms than Mach 0.85 would be at sea level.
Altitude and pressure do not directly affect the speed of sound in air; temperature does. This is why Mach is the meaningful number for aircraft performance, since the aerodynamic effects that matter depend on the ratio rather than the absolute speed.
Multiply by 0.6, which is accurate to within about 3.5%. So 100 km/h is roughly 60 mph against a true 62.1. Going the other way, add 60% to the mph figure.
Because there are 1,000 metres in a kilometre and 3,600 seconds in an hour, and 3,600 divided by 1,000 is 3.6. It is one of the few conversion factors that is both exact and easy to remember.
One nautical mile per hour, which is 1.852 km/h. Because a nautical mile equals one minute of latitude, distances read directly off a navigational chart without conversion, which is why marine and aviation speeds are quoted in knots.
Divide 60 by your pace in minutes per kilometre. A 5:00 min/km pace is 60/5 = 12 km/h. Pace is the reciprocal of speed, so a lower pace number means a faster runner.
No. The speed of sound depends on air temperature, so Mach 1 is about 1,235 km/h at sea level but only around 1,062 km/h at airliner cruising altitude where the air is much colder.