Speed converter
Convert km/h to mph, m/s to km/h, knots, feet per second and Mach with exact factors and a printable two-way speed chart.
- Runs in your browser
- Nothing you enter is sent
- Free, no account
1 km/h = 0.621371192237 mph
Automatic formatting keeps up to 12 significant digits and switches to scientific notation only for numbers past 10¹⁸ or below 10⁻⁹. You can paste values with thousands separators, and fractions such as 3/4 or 1 1/2 are understood too.
mph = km/h ÷ 1.609344
Your value: 1 ÷ 1.609344 = 0.621371192237 mph
Kilometre per hour: Exactly 1000⁄3600 m/s.
Mile per hour: Exactly 0.44704 m/s.
| km/h | mph |
|---|---|
| 1 | 0.621371192237 |
| 5 | 3.10685596119 |
| 10 | 6.21371192237 |
| 20 | 12.4274238447 |
| 30 | 18.6411357671 |
| 40 | 24.8548476895 |
| 50 | 31.0685596119 |
| 60 | 37.2822715342 |
| 70 | 43.4959834566 |
| 80 | 49.709695379 |
| 100 | 62.1371192237 |
| 120 | 74.5645430685 |
| mph | km/h |
|---|---|
| 1 | 1.609344 |
| 5 | 8.04672 |
| 10 | 16.09344 |
| 20 | 32.18688 |
| 30 | 48.28032 |
| 40 | 64.37376 |
| 50 | 80.4672 |
| 60 | 96.56064 |
| 70 | 112.65408 |
| 80 | 128.74752 |
| 100 | 160.9344 |
| 120 | 193.12128 |
| Unit | Symbol | Value in m/s | Notes |
|---|---|---|---|
| Metre per secondMetric | m/s | 1 m/s = 1 m/s | The SI unit of speed. |
| Kilometre per hourMetric | km/h | 1 km/h = 0.277777777778 m/s | Exactly 1000⁄3600 m/s. |
| Mile per hourImperial / US | mph | 1 mph = 0.44704 m/s | Exactly 0.44704 m/s. |
| Foot per secondImperial / US | ft/s | 1 ft/s = 0.3048 m/s | — |
| KnotNautical & aviation | kn | 1 kn = 0.514444444444 m/s | One nautical mile per hour. |
| Mach (sea level)Nautical & aviation | Mach | 1 Mach = 340.29 m/s | Speed of sound in dry air at 15 °C, sea level. It falls to about 295 m/s at cruise altitude, so Mach is not a fixed speed. |
| Speed of lightPhysics | c | 1 c = 299,792,458 m/s | Exact by definition. |
How to convert a speed
- Type the speed into either field. The other one follows immediately, so km/h to mph and mph to km/h are the same tool.
- Pick the units. Metric first, then imperial, then the nautical and aviation units, then the speed of light for the physics questions.
- The chart below gives a full column of values at once, which is easier to scan than converting speed limits one at a time.
The factors, and how to do them in your head
| Conversion | Exact factor | Mental shortcut |
|---|---|---|
| km/h to mph | × 0.6213711922 | Halve it, add 10 % |
| mph to km/h | × 1.609344 | Add 60 % |
| m/s to km/h | × 3.6 | Multiply by 3.6 exactly |
| km/h to m/s | × 5/18 | Divide by 3.6 |
| knots to km/h | × 1.852 | Add 85 % |
| knots to mph | × 1.150779448 | Add 15 % |
Only two of these involve any rounding at all in their definition, and neither does here: the mile is exactly 1,609.344 m and the nautical mile is exactly 1,852 m, so every factor in the table is exact and the converter carries all of it.
Speed limits at a glance
| km/h | mph | Where you see it |
|---|---|---|
| 30 | 18.6 | Urban limits across Europe |
| 50 | 31.1 | Standard built-up limit |
| 60 | 37.3 | US residential and school zones (35–40 mph) |
| 80 | 49.7 | Rural single carriageway |
| 100 | 62.1 | Motorway in much of Europe |
| 112.7 | 70 | UK motorway limit |
| 120 | 74.6 | Spanish and French autoroute |
| 130 | 80.8 | French motorway in dry weather |
Why Mach is not a fixed speed
Mach number is the ratio of an object's speed to the local speed of sound, and sound travels faster in warmer air. At sea level in the international standard atmosphere — 15 °C — sound travels at 340.29 m/s, which is the figure this converter uses. At 11 km, a typical airliner cruising altitude where the air is around −56 °C, it drops to roughly 295 m/s.
That difference is large. An airliner cruising at Mach 0.85 is doing roughly 903 km/h up there, but the same Mach number at sea level would be about 1,041 km/h. Treat any Mach figure from this converter as a sea-level reference value, not as an aviation calculation — real flight planning works from the air temperature at altitude.
Knots, and why sailors and pilots use them
A knot is one nautical mile per hour, and a nautical mile is one minute of latitude. That makes navigation arithmetic trivial on a chart: an aircraft covering 300 nautical miles in an hour is doing 300 knots and has crossed five degrees of latitude. The name comes from the knotted rope once paid out behind a ship to measure its speed against a sand timer.
Questions
How do I convert km/h to mph quickly?
Multiply by 0.621371, or halve it and add ten per cent for a rough figure: 100 km/h ≈ 50 + 12 = 62 mph, against the exact 62.14 mph.
What is a knot?
One nautical mile per hour — exactly 1.852 km/h. It is used at sea and in aviation because a nautical mile is one minute of latitude on a chart.
Is Mach 1 a fixed speed?
No. It is the local speed of sound, which depends on air temperature. This tool uses the sea-level standard of 340.29 m/s; at cruise altitude Mach 1 is nearer 295 m/s.
How do I convert m/s to km/h?
Multiply by 3.6, because there are 3,600 seconds in an hour and 1,000 metres in a kilometre. Dividing by 3.6 goes back the other way.