Convert any speed: road, sea, air and science
This speed converter switches between kilometres per hour, miles per hour, metres per second, knots, feet per second, kilometres per second, Mach and the speed of light. Type one speed and every equivalent appears immediately, together with the factor used, so you can sanity-check a speedometer, a wind forecast or a physics answer at a glance.
Drivers crossing between the UK or US (mph) and India, Europe or Australia (km/h) use it for speed limits; sailors and pilots convert knots; runners and cyclists turn km/h into mph; and students move between km/h and m/s for kinematics problems. All factors are exact apart from Mach, which depends on the air itself — more on that below.
How to use the Speed Converter
- Type a speed in the Value box, such as 100 or 27.5.
- Choose the unit you are converting from in From — search “km/h”, “knot” or “mach”.
- Choose the target unit in To; tap the round swap button to convert the other way.
- Read the answer and formula. Use Precision to round, and Copy to paste the number into notes or a spreadsheet.
- Look through the list of every speed unit, or tap a quick conversion such as “100 km/h → mph”.
Speed Converter features
Road, sea and air units
km/h and mph for driving, knots for boats, aircraft and wind, m/s and ft/s for science and engineering.
Exact where it can be
One mph is exactly 0.44704 m/s and one knot is exactly 1,852 m per hour, so these conversions carry no rounding at all.
Mach reference
Mach 1 is shown at sea level in the International Standard Atmosphere (15 °C), with the caveat clearly explained.
Speed of light
Compare anything with c = 299,792,458 m/s, the exact constant that defines the metre.
Live comparison list
See one speed in all eight units together, grouped by use.
Speed conversion factors
Every speed unit is a distance divided by a time, so its factor comes from the length and time definitions. A kilometre per hour is 1,000 m in 3,600 s; a mile per hour is 1,609.344 m in 3,600 s.
| Unit | Exact value in m/s | Notes |
|---|---|---|
| Kilometre per hour (km/h) | 1/3.6 ≈ 0.2777778 | Road speeds in most countries |
| Mile per hour (mph) | 0.44704 | Road speeds in the US and UK |
| Foot per second (ft/s) | 0.3048 | Ballistics, engineering |
| Knot (kn) | 1,852/3,600 ≈ 0.5144444 | One nautical mile per hour |
| Kilometre per second (km/s) | 1,000 | Spaceflight, orbital speeds |
| Mach 1 (sea level, 15 °C) | 340.294 (reference) | Speed of sound in the standard atmosphere |
| Speed of light (c) | 299,792,458 | Exact, fixed by the SI since 1983 |
Worked examples
km/h to mph — divide by 1.609344. An Indian expressway limit of 120 km/h is 74.6 mph; 50 km/h in a European town is 31.1 mph.
mph to km/h — multiply by 1.609344. The UK motorway limit of 70 mph is 112.65 km/h, and a 30 mph zone is 48.3 km/h.
m/s to km/h — multiply by 3.6. A sprinter averaging 10 m/s is running at 36 km/h. Going the other way, divide by 3.6: 120 km/h is 33.3 m/s.
Knots to km/h — multiply by 1.852. A 30-knot wind is 55.6 km/h (34.5 mph), and an airliner flying at 500 knots over the ground is doing 926 km/h.
Runners usually think in pace rather than speed; the pace calculator turns 12 km/h into 5:00 per kilometre and back.
Why Mach is a moving target
Mach number is a ratio — your speed divided by the local speed of sound — not a fixed speed. Sound travels faster in warm air and slower in cold air, and air gets colder with altitude. The converter uses 340.294 m/s (1,225 km/h or 761 mph), the speed of sound at sea level and 15 °C in the International Standard Atmosphere. At around 11 km, where the standard atmosphere is −56.5 °C, Mach 1 is only about 295 m/s. So treat Mach results here as a sea-level reference, not as an aircraft’s true Mach number at cruising height.
Common speed conversions
| From | To |
|---|---|
| 1 km/h | 0.6213711922 mph |
| 1 mph | 1.609344 km/h |
| 1 m/s | 3.6 km/h |
| 1 m/s | 2.236936292 mph |
| 1 kn | 1.852 km/h |
| 1 kn | 1.150779448 mph |
| 50 km/h | 31.06855961 mph |
| 100 km/h | 62.13711922 mph |
| 70 mph | 112.65408 km/h |
| 1 Mach | 1,225.0584 km/h |
| 1 km/s | 3,600 km/h |
| 1 c | 1,079,252,849 km/h |
Speed Converter FAQ
How do I convert km/h to mph?
Divide by 1.609344, or multiply by about 0.621371. For example, 80 km/h ÷ 1.609344 = 49.7 mph. The speed converter shows the formula with every result.
How do I convert mph to km/h?
Multiply by 1.609344. 60 mph × 1.609344 = 96.56 km/h.
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. 15 m/s × 3.6 = 54 km/h.
What is a knot in km/h and mph?
One knot is one nautical mile per hour: exactly 1.852 km/h, or about 1.1508 mph. Ships, aircraft and wind forecasts for sailors use knots.
How fast is Mach 1?
About 1,225 km/h (761 mph) at sea level at 15 °C. It is slower in cold air, so at airliner cruising heights Mach 1 is roughly 1,060 km/h.
How fast is the speed of light in km/h?
Exactly 299,792,458 m/s, which is about 1.079 billion km/h or 670.6 million mph.