Speed Converter
Convert a speed between km/h, mph, m/s, ft/s, knots and Mach all at once, and turn it into a running pace per kilometre or mile (or a pace back into speed).
100 km/h = 62.14 mph = 27.78 m/s = 54 kn
How Speed Conversion Works
Every speed is a distance divided by a time, so converting means swapping the distance unit, the time unit or both. The converter goes through metres per second. A mile is exactly 1,609.344 m, a nautical mile exactly 1,852 m and a foot exactly 0.3048 m, so every factor below is exact except Mach.
Road Speed Limits in km/h and mph
Driving abroad, or in a car whose speedometer shows the other unit, is the most common reason to convert. A quick rule: km/h × 0.6 is roughly mph, and mph × 1.6 is roughly km/h.
| km/h | mph |
|---|---|
| 30 km/h | 18.6 |
| 50 km/h | 31.1 |
| 80 km/h | 49.7 |
| 100 km/h | 62.1 |
| 110 km/h | 68.4 |
| 120 km/h | 74.6 |
| 130 km/h | 80.8 |
| mph | km/h |
|---|---|
| 20 mph | 32.2 |
| 30 mph | 48.3 |
| 55 mph | 88.5 |
| 65 mph | 104.6 |
| 70 mph | 112.7 |
Running Pace: Speed Turned Upside Down
Runners describe speed as pace: how many minutes it takes to cover a kilometre or mile. Pace is the inverse of speed, so a faster runner has a smaller pace number. Choose a pace unit in the converter to go the other way, from pace to speed.
| Pace /km | Pace /mile | km/h | mph |
|---|---|---|---|
| 4:00 | 6:26 | 15 | 9.32 |
| 4:30 | 7:15 | 13.33 | 8.28 |
| 5:00 | 8:03 | 12 | 7.46 |
| 5:30 | 8:51 | 10.91 | 6.78 |
| 6:00 | 9:39 | 10 | 6.21 |
| 6:30 | 10:28 | 9.23 | 5.74 |
| 7:00 | 11:16 | 8.57 | 5.33 |
| 8:00 | 12:52 | 7.5 | 4.66 |
Worked Example: Pace for a 4-Hour Marathon
A marathon is 42.195 km. What average pace finishes in exactly 4 hours?
Step 1: Average speed
Step 2: Invert to minutes per km
Step 3: Per mile
Hold 5:41 per km (9:09 per mile). Note that 5.69 minutes is 5 minutes 41 seconds, not 5:69. Decimal minutes must be multiplied by 60 to get seconds, which the converter does for you.
Knots and Wind Speed
Ships, aircraft and marine weather forecasts use knots, nautical miles per hour. A knot is a little faster than 1 mph (1.151 mph, or 1.852 km/h). Wind strength is often given on the Beaufort scale, which is defined in knots:
| Beaufort force | Knots | km/h | mph |
|---|---|---|---|
| 0 · Calm | 0–1 | 0–2 | 0–1 |
| 4 · Moderate breeze | 11–16 | 20–30 | 13–18 |
| 6 · Strong breeze | 22–27 | 41–50 | 25–31 |
| 8 · Gale | 34–40 | 63–74 | 39–46 |
| 10 · Storm | 48–55 | 89–102 | 55–63 |
| 12 · Hurricane force | 64+ | 119+ | 74+ |
Why Mach 1 Isn't a Fixed Speed
Mach is speed relative to the speed of sound, and the speed of sound depends on air temperature. This converter uses the standard sea-level value at 15 °C: 340.29 m/s, or about 1,225 km/h (761 mph). At airliner cruising altitudes the air is around −56.5 °C, and Mach 1 drops to about 295 m/s (1,062 km/h). So an aircraft at Mach 0.85 is flying slower in km/h at altitude than the same Mach number would be near the ground.
Frequently asked questions
How do I convert km/h to mph?
Divide by 1.609344, or multiply by 0.621371. For a quick estimate, multiply by 0.6: 100 km/h is about 60 mph (exactly 62.14).
How many km/h is 1 m/s?
Exactly 3.6 km/h, because 1 m/s is 3,600 m in an hour.
Why does a pace of 5:30 not equal 5.30 minutes?
Pace is minutes and seconds. 5:30 is 5.5 minutes. The converter accepts either form: type 5:30 or 5.5.
Is a knot the same as a nautical mile?
No. A nautical mile (1,852 m) is a distance. A knot is a speed: one nautical mile per hour.
Sources
- NIST Special Publication 811: exact definitions of the mile, foot, nautical mile and knot.
- Met Office: Beaufort wind force scale: wind speed ranges in knots.
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