Unit Converters guide
km/h, mph, Knots and Mach: Which Speed Unit Is Used Where
· 3 min read
100 km/h is about 62.1 mph, and 60 mph is about 96.6 km/h. To go from meters per second to kilometers per hour, multiply by 3.6. One knot is one nautical mile per hour, exactly 1.852 km/h. Which unit you need depends on the context: roads, water, air and science each have their own convention.
Which speed unit is used where?
| Context | Usual unit | Why |
|---|---|---|
| Road signs, most countries | km/h | Metric distances on signs |
| Road signs in the US and UK | mph | Distances in miles |
| Ships, aircraft, wind at sea | knots (kn) | Tied to nautical miles and navigation charts |
| Physics, engineering, weather data | m/s | The SI unit of speed |
| Ballistics, sports science (US) | ft/s | Imperial engineering tradition |
| Fast aircraft | Mach | Speed relative to the speed of sound |
How do the conversions work?
Every speed unit is a distance divided by a time, so each conversion combines a length factor and a time factor.
- m/s to km/h: 1 m/s is 3,600 m per hour, or 3.6 km/h. So 10 m/s = 36 km/h, and 12 km/h = 3.33 m/s.
- km/h to mph: divide by 1.609344 (the kilometers in a mile). 100 km/h = 62.14 mph.
- Knots: a nautical mile is 1,852 m, so 1 kn = 1.852 km/h = 1.1508 mph.
- ft/s to mph: 88 ft/s is exactly 60 mph, a handy reference point (5,280 ft × 60 ÷ 3,600 = 88).
Mental shortcuts for the road
- km/h to mph: multiply by 0.6 and add a little. 50 km/h × 0.6 = 30, actual 31.07 mph.
- mph to km/h: multiply by 1.6. 70 mph × 1.6 = 112, actual 112.65 km/h.
Common speed limits, converted:
| km/h | mph |
|---|---|
| 30 | 18.64 |
| 50 | 31.07 |
| 100 | 62.14 |
| 120 | 74.56 |
| 130 | 80.78 |
| mph | km/h |
|---|---|
| 20 | 32.19 |
| 60 | 96.56 |
| 70 | 112.65 |
Speedometers in many cars show both scales. If yours doesn't, these tables cover most limits you will meet.
Knots on the water and in the air
Knots make navigation easy: one nautical mile was originally one minute of latitude, so speed and position on a chart share a unit. A sailing boat doing 25 knots is moving at 12.86 m/s. A jet cruising at 450 knots is doing 833.4 km/h relative to the air around it; ground speed differs with the wind.
What is Mach, exactly?
Mach is speed divided by the local speed of sound. Because the speed of sound depends on air temperature, Mach 1 is not a fixed number of km/h. The converter uses the standard sea-level value of 340.29 m/s, which makes Mach 1 = 1,225 km/h or 761.2 mph. At cruising altitude, where the air is much colder, Mach 1 is noticeably slower, so treat Mach conversions here as a sea-level reference.
How to use the Speed Converter
The Speed Converter handles six units:
- Enter a speed in Value.
- Choose From and To: meters per second, kilometers per hour, miles per hour, feet per second, knots or Mach (sea level). Use ⇄ to swap.
- Read the converted speed, or the table underneath showing the speed in all six units at once.
Results are shown with up to 10 significant digits.
What about running pace?
Runners often use pace, minutes per kilometer or per mile, which is time divided by distance, the inverse of speed. The converter doesn't calculate pace directly, but you can get there: 12 km/h means 12 km in 60 minutes, so 60 ÷ 12 = 5:00 per km. For distances, the Length Converter converts kilometers and miles, and the Time Converter handles minutes, hours and seconds.
FAQ
Is a knot the same as a mile per hour?
No. A knot is a nautical mile per hour, about 15% faster than 1 mph.
Why is m/s used in weather data?
It is the SI unit, so scientific models and many weather services use it. To get a feel for wind speeds, multiply by 3.6 for km/h: a 10 m/s wind is 36 km/h.
How fast is the speed of light in these units?
Exactly 299,792,458 m/s, which is about 1,079,252,849 km/h or roughly 670.6 million mph. Enter it in m/s to see it in every unit.
Convert road, sea, air and lab speeds with the Speed Converter.