Speed Converter
Convert between meters per second, km/h, mph, knots, Mach and more.
How speed conversion works
Speed is distance divided by time. The SI unit for speed is meters per second (m/s), which serves as the base for all conversions on this page. Every other unit is expressed as a fixed number of m/s, so converting between any two units is a single multiplication and division.
Result = Input × (From unit in m/s) ÷ (To unit in m/s)Worked examples:
Convert 100 km/h to mph:
100 × 0.277778 ÷ 0.44704 = 62.137 mph
Convert 60 mph to m/s:
60 × 0.44704 ÷ 1 = 26.822 m/s
Convert Mach 2 to km/h:
2 × 340.29 ÷ 0.277778 = 2450.9 km/hUnit reference: all speed units explained
| Unit | In m/s | Primarily used in |
|---|---|---|
| Meters/second (m/s) | 1 (base unit) | Science, physics, athletics (sprints) |
| Kilometers/hour (km/h) | ≈ 0.2778 m/s | Road speed limits worldwide (except US/UK) |
| Miles/hour (mph) | ≈ 0.4470 m/s | Road speed limits in the US and UK |
| Feet/second (ft/s) | 0.3048 m/s | Engineering, ballistics, US aviation |
| Knots (nautical miles/hr) | ≈ 0.5144 m/s | Aviation and maritime navigation globally |
| Mach | ≈ 340.29 m/s at sea level | Supersonic aircraft, aerospace engineering |
Mach number: why it changes with altitude
The Mach number is the ratio of an object's speed to the local speed of sound — and the speed of sound is not constant. At sea level (15°C, standard atmosphere), sound travels at approximately 340 m/s (1,225 km/h). At 35,000 feet cruising altitude where the air is around −57°C, it drops to about 295 m/s (1,062 km/h).
This means a commercial aircraft cruising at Mach 0.85 travels at about 903 km/h at altitude, but the same Mach 0.85 at sea level would be 1,041 km/h. This converter uses the sea-level standard value of 340.29 m/s per Mach, which is the conventional reference for most general-purpose calculations.
Speed of sound at sea level (15°C): 340.29 m/s = 1,225 km/h = 661.5 kn
Speed of sound at 35,000 ft (−57°C): 295 m/s = 1,062 km/h = 573.6 kn
Concorde cruise speed: Mach 2.04
= 2.04 × 340.29 = ~694 m/s = ~2,498 km/hKnots: the unit aviation and shipping share
A knot is one nautical mile per hour. Because one nautical mile equals one arcminute of latitude (1,852 m), pilots and navigators can read their speed directly off a chart in terms of Earth's geography — no conversion needed. At 450 knots, an aircraft covers 450 arcminutes of latitude per hour.
Knots are used by all commercial aviation, maritime vessels, and military aircraft worldwide, regardless of whether the country uses metric or imperial units for road speeds. The unit is one of the few that has survived metrication entirely intact because of this navigation convenience.
Common real-world uses
Tips for speed conversion
- Quick km/h to mph mental shortcut: Divide by 1.6 (or multiply by 0.625). So 80 km/h ≈ 50 mph, 120 km/h ≈ 75 mph. The exact factor is 1.60934, so rounding adds a small error — acceptable for everyday estimation, not for navigation.
- m/s to km/h: Multiply by 3.6 (since 1 m/s = 3,600 m/h = 3.6 km/h). Conversely, divide km/h by 3.6 to get m/s. This is the most useful conversion in physics and sports science.
- Mach is not a fixed speed. If an aircraft data sheet says "maximum Mach 0.92" without specifying altitude, assume it refers to cruise altitude (≈ 295 m/s per Mach), not sea level (340 m/s). The difference is about 15%.
- Pace vs. speed are inverses. A running pace of 5:00 min/km means the runner covers 1 km in 5 minutes, which equals a speed of 12 km/h or 3.33 m/s. Speed and pace are reciprocals — converting between them requires dividing 60 (minutes) by the pace value, not multiplying.
Frequently asked questions
How do I convert km/h to mph?
Multiply kilometers per hour by 0.621. For example, 100 km/h × 0.621 = 62.1 mph.
What is a knot?
A knot is one nautical mile per hour, equal to about 1.852 km/h or 1.151 mph. It is used in maritime and aviation contexts.
How do I convert m/s to km/h?
Multiply meters per second by 3.6. For example, 10 m/s × 3.6 = 36 km/h.
Why are aircraft and ships measured in knots?
Knots relate directly to nautical miles, which are based on the Earth's lines of latitude, making navigation calculations simpler at sea and in the air.
All speeds convert through meters/second (m/s). Click any tile to use that value as new input.