Speed Converter
Convert between miles per hour, kilometres per hour, metres per second, knots, feet per second, Mach and the speed of light. This tool is useful for driving, running, cycling, aviation, marine speeds, physics, engineering and quick metric-to-imperial checks. Enter a value in any speed unit and every other unit updates in real time, with reference speeds and formulas to help you check the result.
Convert speed
Choose any input box, enter a speed, and the calculator converts it through metres per second as the base unit. This keeps mph, km/h, m/s, knots, feet per second, Mach and speed-of-light comparisons consistent across the page.
Quick references
Full conversion table
Speed reference guide
Conversion formulas
How it works
This converter uses metres per second as the central base unit. When you enter a value, the calculator first converts that value into m/s, then converts the m/s value into every other speed unit shown on the page. This avoids inconsistent chained conversions and keeps road, running, aviation, marine and physics units aligned.
Most speed conversions are ratio-based. For example, miles per hour to kilometres per hour uses a fixed conversion factor, while m/s to km/h multiplies by 3.6. Mach is included as an approximate comparison based on the speed of sound at sea level, but the actual speed of sound changes with temperature, altitude and air conditions.
Formula used
For most speed conversions, the calculator uses this two-step formula:
converted value = value in m/s ÷ m/s factor of target unit
Common factors include: 1 mph = 0.44704 m/s, 1 km/h = 0.277777... m/s, 1 m/s = 3.6 km/h, 1 knot ≈ 0.514444 m/s, 1 ft/s = 0.3048 m/s and the speed of light = 299,792,458 m/s.
Worked example
Example: convert 70 mph to km/h
Miles per hour to kilometres per hour uses the factor 1.60934.
So, 70 mph is about 112.65 km/h.
Example: convert 10 m/s to km/h
Metres per second to kilometres per hour multiplies by 3.6.
So, 10 m/s is 36 km/h.
Common mistakes
Mixing mph and km/h
A speed of 70 mph is about 113 km/h, not 70 km/h. This matters for driving, journey estimates and road-speed comparisons.
Confusing knots with mph
Knots are nautical miles per hour. They are commonly used in aviation and marine settings and are not the same as mph.
Treating Mach as fixed in all conditions
Mach depends on the local speed of sound, which changes with temperature and altitude. This page uses an approximate sea-level value.
Rounding too early
For physics, engineering or aviation calculations, keep more decimal places during calculation and round only the final result.
Common questions
How many km/h is 1 mph? ⌄
How do I convert m/s to km/h? ⌄
What is a knot? ⌄
Is Mach always 343 m/s? ⌄
Sources, assumptions and disclaimer
This converter is intended for general everyday use, study, journey planning, running/cycling comparisons and quick physics or engineering checks. Results are rounded for readability and should be checked against official documentation for safety-critical, aviation, marine, motorsport or engineering use.
- Base unit: conversions are handled through metres per second.
- Road-speed conversions: mph and km/h use standard fixed relationships.
- Knots: knot conversions are based on one nautical mile per hour.
- Mach assumption: Mach is estimated using 343 m/s as an approximate speed of sound at sea level. Actual Mach speed changes with atmospheric conditions.
- Speed of light: the speed of light is treated as 299,792,458 m/s for comparison.
- Safety disclaimer: do not use speed conversion alone for driving decisions, stopping distances, aviation planning, marine navigation or legal compliance.