Speed Converter
Convert between mph, km/h, m/s, feet per second and knots instantly.
Convert speed and velocity units
This speed converter switches instantly between the units used for driving, running, sailing, and science: miles per hour (mph), kilometres per hour (km/h), metres per second (m/s), feet per second (ft/s), and knots. It is handy for converting car speeds between the US/UK and the rest of the world, reading marine and aviation speeds in knots, or working out pace in physics problems.
Common speed conversions
| From | To | Result |
|---|---|---|
| 1 mph | km/h | 1.609 km/h |
| 60 mph | km/h | 96.56 km/h |
| 100 km/h | mph | 62.14 mph |
| 1 knot | mph | 1.151 mph |
| 1 m/s | km/h | 3.6 km/h |
What is a knot?
A knot is one nautical mile per hour, used in shipping and aviation. One knot equals about 1.151 mph or 1.852 km/h. Because nautical miles are based on the Earth’s circumference, knots are convenient for navigation over long distances.
Frequently asked questions
How do I convert mph to km/h?
Multiply miles per hour by 1.609 to get kilometres per hour. For example, 70 mph is about 112.7 km/h.
How fast is 100 km/h in mph?
About 62 mph. Multiply any km/h value by 0.621 to convert it to mph.
How do I convert km/h to metres per second?
Divide by 3.6. There are 1,000 metres in a kilometre and 3,600 seconds in an hour, so 1 km/h is 1,000 ÷ 3,600 = 0.2778 m/s. For example, 90 km/h is 25 m/s. To go the other way, multiply m/s by 3.6.
What is the speed of sound in mph?
In dry air at 20 °C, sound travels at about 343 m/s, which is roughly 1,235 km/h or 767 mph. It is slower in colder air, which is why the speed of Mach 1 for aircraft depends on altitude.
Exact speed conversion factors
Every unit in the converter is stored as a multiple of one metre per second, the SI unit of speed. These factors follow directly from the exact definitions of the mile (1,609.344 m), the foot (0.3048 m) and the nautical mile (1,852 m).
| Unit | In metres per second | In km/h |
|---|---|---|
| 1 m/s | 1 | 3.6 |
| 1 km/h | 0.27778 | 1 |
| 1 mph | 0.44704 (exact) | 1.609344 |
| 1 ft/s | 0.3048 (exact) | 1.09728 |
| 1 knot | 0.51444 | 1.852 (exact) |
How to calculate speed
Average speed is distance divided by time. If you drive 150 miles in 2 hours 30 minutes, first turn the time into hours (2.5 h), then divide: 150 ÷ 2.5 = 60 mph. To express that in km/h, multiply by 1.609344: 60 × 1.609344 = 96.56 km/h. You can rearrange the same formula to find time (distance ÷ speed) or distance (speed × time).
Worked example: a sprinter’s average speed
- The 100 m world record is 9.58 seconds.
- Average speed: 100 ÷ 9.58 = 10.44 m/s.
- In km/h: 10.44 × 3.6 = 37.58 km/h.
- In mph: 10.44 ÷ 0.44704 = 23.35 mph.
For runners who think in minutes per kilometre or per mile rather than speed, the athletic pace converter is the better tool, and our guide to min/km to min/mile pace conversion explains the maths.
UK speed limits in km/h
UK road signs use miles per hour, which can confuse visiting drivers used to kilometres per hour. Here are the standard limits for cars converted to km/h.
| Road type | Limit (mph) | Equivalent (km/h) |
|---|---|---|
| 20 mph zone | 20 | 32.2 |
| Built-up area | 30 | 48.3 |
| Single carriageway | 60 | 96.6 |
| Dual carriageway and motorway | 70 | 112.7 |
Lower limits apply to vans, lorries and vehicles towing trailers, and local signs always take priority.
Quick mental shortcuts
- mph to km/h: multiply by 8 and divide by 5. 50 mph is about 80 km/h (exact 80.47).
- km/h to mph: multiply by 5 and divide by 8. 120 km/h is about 75 mph (exact 74.56).
- m/s to mph: roughly double and add 10%. 20 m/s is about 44 mph (exact 44.74).
- Knots to mph: add 15%. 40 knots is about 46 mph.
Speed vs velocity
Speed tells you how fast something moves; velocity also tells you which direction. A car going round a roundabout at a steady 20 mph has constant speed but changing velocity. Both use the same units, so this converter works for either. For acceleration, force and energy problems, see the physics calculator, and for distances use the length converter.