Car dashboards, weather forecasts, marine charts and physics homework all measure the same thing in four different units — and knots, the one used at sea and in the air, is the one most converters leave out.
What the Speed Converter does
Converts between m/s, km/h, mph, knots and ft/s using exact factors relative to metres per second.
A knot is one nautical mile per hour — exactly 0.5144444… m/s. Because a nautical mile is a minute of latitude, a vessel at 30 knots covers half a degree of latitude an hour, which is why the unit survives.
Open the Speed Converter and follow the settings and checks below.
Exact factors, in metres per second
| Setting | What it means |
|---|---|
| m/s | 1 — the SI unit |
| km/h | 0.2777… — that is 1/3.6 |
| mph | 0.44704 — exact |
| Knot | 0.5144444… — one nautical mile per hour |
| ft/s | 0.3048 — exact |
| Quick check | km/h ÷ 3.6 = m/s |
| Rough check | Knots × 1.15 ≈ mph |
| Default conversion | mph → km/h |
How to use it
- Enter the speed.
- Choose the unit you have and the unit you want.
- Read every unit at once.
Practical advice
Divide km/h by 3.6 to get m/s. It is exact rather than approximate, and it is the conversion that comes up constantly in physics problems where speeds are quoted in km/h and every formula expects m/s. 90 km/h is exactly 25 m/s.
Common questions
What exactly is a knot?
One nautical mile per hour, so about 1.15 mph or 1.85 km/h. It persists because a nautical mile is one minute of latitude, making speed and position arithmetic straightforward on a chart.
How do I convert km/h to m/s in my head?
Divide by 3.6. That is exact — there are 3600 seconds in an hour and 1000 metres in a kilometre, so the factor is 1000/3600.
Is mph exactly defined?
Yes. A mile is exactly 1609.344 m and an hour is 3600 seconds, so one mph is exactly 0.44704 m/s. All the factors here are exact rather than rounded.
Where is ft/s used?
Mostly US engineering and ballistics, where muzzle velocities are conventionally quoted in feet per second. It is otherwise rare in everyday use.
Useful next tools
- Unit Converter — Length, mass, temperature, area, volume, speed and data.
- Length Converter — Convert miles, km, feet, inches, metres and more.
- Running Pace Calculator — Pace, speed and race times from a distance and time.
- Travel Time Calculator — How long a trip takes from distance and average speed.
- Fuel Economy Converter — Convert between MPG, L/100km and km/L.
- Temperature Converter — Convert Celsius, Fahrenheit and Kelvin.
Vootkit provides a browser calculator and educational guidance. Results depend on the values and units you enter, so verify important financial, academic, safety or professional decisions with an appropriate authoritative source.
Try the tools from this guide
Keep reading
How to Calculate Exact Age and Date Difference
Gives the gap between two dates as years, months and days, and also as a total in days, weeks and hours.
How to Convert Square Metres, Feet, Acres and Hectares
Converts between metric and imperial area units using exact squared factors. A square foot is 0.09290304 m² — which is 0.3048 squared, not 0.3048.
How to Generate a Barcode That Works
Generates a scannable barcode in CODE128, EAN-13, UPC-A or CODE39 from whatever value you enter.