Speed Converter
Convert speed between metres per second, kilometres per hour, miles per hour, knots, and feet per second.
How to use this tool
- Enter speed and from unit in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your miles/hour and the full breakdown beneath it.
Formula
All units convert to metres per second (m/s) first, then to the target unit:
m/s = input × factorfrom
output = m/s ÷ factorto
Key factors: m/s = 1 | km/h = 1/3.6 m/s | mph = 0.44704 m/s | knot = 0.514444 m/s | ft/s = 0.3048 m/s
How it works
The converter normalises speed to metres per second, the SI unit, then divides by the m/s equivalent of each target unit. The km/h factor of 1/3.6 arises because 1 km = 1000 m and 1 hour = 3600 s, so 1 km/h = 1000/3600 = 1/3.6 m/s.
A common mistake is confusing knots with km/h: a knot is one nautical mile per hour (1852 m/h ≈ 0.5144 m/s), which is roughly 1.852 km/h — not 1 km/h. Pilots and mariners who manually convert between knots and km/h often underestimate speeds by nearly half if they treat them as equivalent.
Worked example
Convert 100 km/h to all speed units
- Input: 100 km/h (from_unit = kmh), so base in m/s = 100 × (1/3.6) = 100 / 3.6 ≈ 27.7778 m/s.
- km/h: 27.7778 / (1/3.6) = 100 km/h (identity check).
- mph: 27.7778 / 0.44704 ≈ 62.1371 mph.
- Knots: 27.7778 / 0.514444 ≈ 53.9957 kn. Feet/second: 27.7778 / 0.3048 ≈ 91.1344 ft/s.
27.7778 m/s | 100 km/h | 62.1371 mph | 53.9957 kn | 91.1344 ft/s
Common mistakes to avoid
- Treating knots as kilometres per hour -- 1 knot is 1.852 km/h, not 1 km/h; confusing the two in aviation or maritime contexts causes significant navigation errors.
- Confusing miles per hour with metres per second -- 60 mph is about 26.8 m/s, not 60 m/s.
- Forgetting that speedometer readings in mph versus km/h differ by about 61% -- driving in Canada or Europe after a US road trip can produce a genuinely unsafe speed error.
Key terms
- Metre per second (m/s)
- The SI unit of speed. 1 m/s is approximately 3.6 km/h or 2.237 mph.
- Knot (kn)
- A unit of speed equal to one nautical mile per hour (1.852 km/h). Used in maritime and aviation navigation.
- Miles per hour (mph)
- An imperial speed unit equal to 0.44704 m/s, used for road speeds in the US and UK.
- Nautical mile
- A unit of distance equal to 1852 metres, defined as one minute of arc of latitude. Forms the basis for the knot.
Frequently asked questions
- How fast is 100 km/h in mph?
- 100 km/h is approximately 62.14 mph. A quick mental estimate is to multiply km/h by 0.621.
- What is a knot and why is it used in navigation?
- A knot is one nautical mile per hour (1.852 km/h or about 1.151 mph). It is used in aviation and maritime navigation because nautical miles correspond directly to minutes of latitude, simplifying position calculations.
- What is the speed of sound in different units?
- At sea level and 20 degrees C, the speed of sound is approximately 343 m/s, 1,235 km/h, 767 mph, or 667 knots. It varies with temperature and medium.