Speed Converter
Convert between mph, km/h, m/s, knots and ft/s instantly.
Convert from:
Common speeds:
| Unit | Amount |
|---|---|
| Miles per hour | — mph |
| Kilometres per hour | — km/h |
| Metres per second | — m/s |
| Knots | — kn |
| Feet per second | — ft/s |
Speed is measured in different units depending on context — km/h and mph for road travel, knots in aviation and at sea, m/s in physics and engineering. The confusion is most acute when crossing between countries with different conventions, or switching between domains like driving and flying.
Quick reference
- mph → km/h: multiply by 1.60934 (approx. ×1.6)
- km/h → mph: multiply by 0.62137 (approx. ×0.62)
- km/h → m/s: divide by 3.6
- m/s → km/h: multiply by 3.6
- knots → km/h: multiply by 1.852 (exact)
- knots → mph: multiply by 1.15078
- mph → knots: multiply by 0.86898
- ft/s → mph: multiply by 0.68182
When do you need this?
- Renting a car abroad and reading speed limit signs in unfamiliar units
- Following aviation weather reports or air traffic data that use knots
- Reading a European car's speedometer in km/h when used to mph
- Physics or engineering problems where m/s is required
- Tracking a ship's speed or tide flow in knots
- Comparing athletic performance data between metric and imperial records
Common speed reference
| Speed | km/h | mph | m/s |
|---|---|---|---|
| Walking | 5 | 3.1 | 1.4 |
| Cycling | 15 | 9.3 | 4.2 |
| City speed limit | 50 | 31 | 13.9 |
| Motorway | 100 | 62 | 27.8 |
| High-speed train | 300 | 186 | 83.3 |
| Speed of sound | 1,235 | 767 | 343 |
Understanding the units
Miles per hour (mph)
Miles per hour is the standard road speed unit in the United States, the United Kingdom, and a handful of other countries. One mile equals 1,609.34 metres. Road signs, speedometers and speed cameras in these countries all use mph.
Kilometres per hour (km/h)
Kilometres per hour is the metric standard used in most of the world. One kilometre is exactly 1,000 metres. Speed limits across Europe, Asia, Australia and South America are given in km/h. It is also the unit used in most weather systems for wind speed outside the US.
Metres per second (m/s)
Metres per second is the SI unit of speed and is used in physics, engineering and scientific contexts. It is rarely seen on road signs but is essential for calculations involving force, kinetic energy and fluid dynamics. To convert from km/h, divide by 3.6.
Knots (kn)
A knot is one nautical mile per hour. One nautical mile is exactly 1,852 metres — corresponding to one arc-minute of latitude on the Earth's surface. Knots are the universal standard for aviation and maritime navigation because they tie speed directly to geographic coordinates. One knot equals exactly 1.852 km/h.
Feet per second (ft/s)
Feet per second is an imperial unit of speed used mainly in ballistics, acoustics, and some US engineering contexts. It is rarely encountered in everyday life but appears in specifications for projectile velocity, water flow and pipe systems.
Common mistakes
- Confusing mph and km/h on rental cars: A car showing 100 on the dial could be 100 km/h (62 mph) or 100 mph (161 km/h) depending on where it is registered. Always check the speedometer label before driving.
- Using knots and km/h interchangeably in aviation: A wind speed of 20 knots is 37 km/h — not 20 km/h. Mixing these up affects fuel calculations and flight planning.
- Forgetting to divide by 3.6 for m/s: It is easy to assume 1 km/h = 1 m/s. In reality, 1 km/h = 0.278 m/s. Always divide by 3.6.
- Using the rough ×1.6 shortcut in precision contexts: ×1.6 gives an error of about 0.6%. Fine for reading a sign, not for engineering or aviation calculations where 1.60934 is needed.
- Assuming Mach 1 is constant: The speed of sound — and therefore Mach 1 — changes with altitude and temperature. At cruising altitude (~35,000 ft) Mach 1 is around 1,062 km/h, not the sea-level 1,235 km/h.
Which should you use?
- Driving in the US or UK: mph — all road signs and legal limits are in mph.
- Driving anywhere else: km/h — it is the legal and posted standard.
- Flying or sailing: knots — every instrument, controller and chart uses knots.
- Physics or engineering calculations: m/s — it is the SI base unit and works directly with Newton's laws and energy equations.
- Weather reports: km/h in most of the world; mph in the US; knots in aviation forecasts.
Frequently asked questions
How do I convert mph to km/h?
Multiply mph by 1.60934 to get km/h. For a quick approximation, multiply by 1.6. So 60 mph is about 96.6 km/h. To reverse, divide km/h by 1.60934 (or multiply by 0.621).
What is 100 km/h in mph?
100 km/h equals 62.1 mph. This is the motorway speed limit in many European countries. Divide any km/h value by 1.60934 to get mph.
What is a knot and why is it used in aviation?
A knot is one nautical mile per hour, where one nautical mile equals 1,852 metres — one arc-minute of latitude. Aviation uses knots because navigating by latitude and longitude makes nautical miles a natural unit of distance, so speed in knots directly corresponds to how quickly you cover degrees on a chart.
How do I convert km/h to m/s?
Divide km/h by 3.6 to get m/s. For example, 90 km/h ÷ 3.6 = 25 m/s. To go from m/s back to km/h, multiply by 3.6. This comes up often in physics problems and engineering calculations.
How fast is the speed of sound in km/h and mph?
The speed of sound in dry air at 20°C is 343 m/s, which is about 1,235 km/h or 767 mph. It decreases with altitude as air gets colder. Aircraft speed as a fraction of the speed of sound is expressed as a Mach number — Mach 1 is the speed of sound, Mach 2 is twice that.
Why do the US and UK use mph instead of km/h?
The US and UK retained imperial units — including miles — as their road measurement standard. Most of the world adopted the metric system and uses km/h. The UK officially uses km/h in some technical and scientific contexts but miles per hour for road speed limits. Aviation and maritime worldwide use knots regardless of country.
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