Speed Converter
Convert between mph, km/h, m/s, knots and Mach — from walking pace to the speed of light. Includes all UK road speed limits.
SPEED CONVERTER
Common units
Specialist units
Enter a speed to see a real-world comparison
🇬🇧 UK road speed limits
Famous speeds — click to load
Step-by-step solution
Type a speed to see the conversion working
The ÷ 3.6 trick
The most common speed conversion: km/h ↔ m/s. Divide km/h by 3.6 to get m/s, or multiply m/s by 3.6 to get km/h. This comes from the fact that 1 km = 1,000 m and 1 hour = 3,600 s, so 1 km/h = 1000/3600 m/s = 1/3.6 m/s.
Key conversion facts
Real-world speeds
Speed Converter Explained
Core concepts, classroom applications, and plain-English explanations for all audiences.
When would you actually use this?
You hire a car in France and the speed limit signs show 130 km/h on the motorway. What's that in mph? (About 81 mph.) Or you read that Usain Bolt's 100 m world record is 9.58 s — that's 10.44 m/s, which converts to 37.6 km/h or 23.4 mph. Any time you cross between unit systems, conversion is essential.
Worked example
"A motorway has a 70 mph limit. A foreign driver needs to know this in km/h."
1 mile = 1.60934 km
70 mph × 1.60934 = 112.65 km/h
Quick check: 70 × 1.6 = 112 ✓
Shortcut: km/h ÷ 1.6 ≈ mph; mph × 1.6 ≈ km/h. Close enough for everyday use.
Unit reference
- → m/s — the SI unit. Used in science, physics calculations, and athletics timing.
- → km/h — everyday road speed in most of the world.
- → mph — used in the UK and USA for road speeds.
- → knots — nautical miles per hour; used in aviation and sailing.
m/s to km/h
Multiply by 3.6 (there are 3,600 seconds in an hour and 1,000 m in a km: 3600 ÷ 1000 = 3.6). Divide by 3.6 to go the other way.
Speed Converter: Understand and Convert Speed Units
Our Speed Converter is an essential tool for anyone needing to switch between different units of speed quickly and accurately. Whether you're a GCSE Physics student tackling motion problems, a driver planning a trip through Europe, or simply curious about how fast things move, this calculator has you covered.
We provide live conversions between the most common speed units: miles per hour (mph), kilometres per hour (km/h), metres per second (m/s), knots, feet per second (ft/s), and Mach (the speed of sound). With a focus on UK users, you'll find familiar units like mph alongside international standards like km/h, crucial for understanding speed limits abroad. Explore real-world comparisons, from the leisurely pace of a snail to the incredible velocity of the International Space Station, to truly grasp the scale of different speeds.
Common mistakes to avoid
- Thinking 1 km/h is roughly 1 m/s:Many people underestimate the difference between these units, especially when converting quickly in their head. 1 km/h is actually 1/3.6 m/s, or approximately 0.278 m/s. So, 3.6 km/h is 1 m/s.
- Assuming a knot is the same as a kilometre per hour:Both are metric-ish units, but knots are based on nautical miles, not kilometres. A knot is one nautical mile per hour. One nautical mile is 1.852 km, so 1 knot is 1.852 km/h (or 1.151 mph).
- Believing Mach 1 is always a fixed speed, like 343 m/s:The speed of sound (and thus Mach 1) changes with the medium it travels through, primarily temperature and altitude. Mach 1 is the speed of sound, which varies. 343 m/s is only accurate for dry air at 20°C at sea level. At higher altitudes or different temperatures, Mach 1 will be different.
- Assuming a speed limit of '50' in Europe is similar to '50' in the UK:UK limits are in miles per hour (mph), while most of Europe uses kilometres per hour (km/h). A '50' sign means very different speeds. 50 mph is approximately 80 km/h. So, 50 km/h is significantly slower than 50 mph, roughly 31 mph.