Speed Converter
Convert between km/h, mph, knots, and m/s in one step. Whether you're reading a foreign speed sign, filing a sailing log, or checking wind speeds for a weather model — get a precise answer in under a second.
What This Tool Does
The conversion
Enter any speed value in one unit and the converter instantly recalculates it in all three others. The math uses exact internationally agreed conversion factors — 1 mile = 1.609344 km, 1 nautical mile = 1852 m — carried through at 64-bit floating-point precision, so rounding errors stay well below anything that matters in practice.
Who uses it
- Drivers crossing between metric and imperial countries (EU ↔ UK / US)
- Sailors & pilots translating knot-based forecasts into familiar units
- Students & researchers working with SI units (m/s) for physics problems
- Athletes comparing pace data from GPS devices in different formats
- Developers & QA spot-checking speed-related data in apps and APIs
Understanding the Four Units
km/h
Kilometres per hour
The metric standard for road speed. Used on speed limit signs across Europe, Asia, Australia, and most of Africa and South America. A car at 100 km/h covers 100 km in exactly one hour.
mph
Miles per hour
The imperial unit used on road signs in the United States, United Kingdom, and a few other countries. One mph equals 1.609344 km/h — the conversion factor is exact by international definition.
knots
Nautical miles per hour
The universal unit for maritime and aviation speeds. One knot = 1 nautical mile per hour = 1.852 km/h. Wind speeds in official weather and METAR reports are almost always in knots.
m/s
Metres per second
The SI base unit for velocity, used in physics, engineering, and scientific research. Wind speeds from weather stations and anemometers are often reported in m/s in continental Europe and scientific literature.
Worked Examples
Real conversions you might need — check them against the tool above.
You rent a car in Germany and see a 130 km/h autobahn sign.
→ 130 km/h = 80.8 mph. Safely within the 85 mph comfort range for most North American drivers.
A marine weather bulletin warns of 35-knot winds.
→ 35 knots ≈ 64.8 km/h or 40.3 mph — a Force 7 near-gale on the Beaufort scale. Small craft should seek shelter.
A physics problem asks you to convert 20 m/s to km/h.
→ 20 m/s × 3.6 = 72 km/h. (Multiply m/s by 3.6 to get km/h — the converter does this automatically.)
A cyclist averages 28 mph on a sportive and wants to report in km/h.
→ 28 mph × 1.609344 = 45.06 km/h.
Quick Reference: Base Unit Conversions
All factors are rounded to 4 decimal places for readability. The tool above uses full precision.
| Starting unit | mph | Knots | m/s |
|---|---|---|---|
| 1 km/h | 0.6214 | 0.5400 | 0.2778 |
| 1 mph | 1 | 0.8690 | 0.4470 |
| 1 knot | 1.1508 | 1 | 0.5144 |
| 1 m/s | 2.2369 | 1.9438 | 1 |
Real-World Speed Reference
Common speeds as context for your conversions.
| Speed | km/h | mph | Knots | m/s |
|---|---|---|---|---|
| Walking pace | 5 | 3.1 | 2.7 | 1.4 |
| City speed limit (typical) | 50 | 31.1 | 27.0 | 13.9 |
| Motorway / highway limit | 120 | 74.6 | 64.8 | 33.3 |
| Cruising airliner | 900 | 559.2 | 486.0 | 250.0 |
| Speed of sound (sea level, 20 °C) | 1235 | 767.3 | 667.0 | 343.0 |
Tips & Limitations
💡 Tips for best results
- Decimals welcome: Enter values like
55.5— the converter handles them without rounding. - Knots vs km/h for wind: Aviation METARs use knots; European weather maps often use m/s. Bookmark this page for quick on-the-fly lookups.
- m/s shortcut: To mentally estimate m/s from km/h, divide by 3.6. Exact: ÷ 3.6 = m/s.
- GPS pace vs speed: Running GPS watches often show min/km or min/mile, which is pace, not speed. Speed is the reciprocal — a separate calculation.
⚠️ Limitations to know
- Speed of sound varies: The reference in the table above is at 20 °C at sea level. At altitude or different temperatures it changes significantly — Mach numbers require a separate, context-aware calculator.
- Not for certified operations: Aviation and maritime navigation decisions must rely on certified instruments and official charts, not a web tool.
- Pace is not speed: This tool converts speed units only. Converting running or cycling pace (min/km) to m/s requires an extra step.
Frequently Asked Questions
What is a knot and why is it still used?
A knot is one nautical mile per hour (1.852 km/h). Nautical miles are based on arc-minutes of latitude, which makes chart navigation on a sphere much simpler — one nautical mile equals one arc-minute. Mariners and pilots keep using knots because it directly links speed to angular position on Earth, a relationship that has never stopped being useful.
How do I convert mph to km/h by hand?
Multiply by 1.609344. A rough mental trick: multiply by 1.6, then add 1% of the original. So 60 mph → 60 × 1.6 = 96, + 0.6 ≈ 96.6 km/h. The exact answer is 96.56 km/h.
What is m/s used for?
Metres per second is the SI base unit for speed and appears in physics equations, engineering calculations, and scientific papers. It is also used for wind speed in many European countries and is the standard in meteorological data from ground stations and radiosondes.
Is this accurate enough for aviation planning?
The converter uses exact, internationally standardised conversion factors and JavaScript's 64-bit double-precision arithmetic, giving results accurate to at least 12 significant figures — far beyond any practical need. That said, all flight operations must rely on certified avionics and official publications. This tool is for reference and education.
Does this tool store my data?
No. The converter runs entirely in your browser. No input value ever leaves your device, and nothing is logged on our servers.
What is the difference between speed and velocity?
Speed is a scalar (magnitude only — e.g. 100 km/h). Velocity is a vector (magnitude + direction — e.g. 100 km/h north-east). This converter works with speed. Direction is outside its scope.
How the Converter Works
Every conversion passes through metres per second as an internal base unit. When you type a value, it is first converted to m/s using an exact factor, then fanned out to all three output units in a single pass. This two-step normalisation prevents cumulative rounding that would appear if conversions were chained (e.g. km/h → mph → knots).
The exact factors used: 1 mph = 0.44704 m/s (exact, from the international yard definition); 1 km/h = 1/3.6 m/s (exact); 1 knot = 1852/3600 m/s (exact, from the international nautical mile). No approximations are introduced.