How to use it
- Type a speed. Decimals, commas and scientific notation all work.
- Choose the unit you have and the unit you want, or press the swap button to flip them.
- Scroll to the road: the lane markings pass the car at the speed you entered. Use the pause button to stop the motion.
How the conversion works
Every speed unit is a length divided by a time, and each length is defined exactly in meters, so every factor is exact:
1 mph = 1,609.344 m ÷ 3,600 s = 0.44704 m/s (exact)
1 km/h = 1,000 m ÷ 3,600 s = 1/3.6 m/s (exact)
1 mph = 1.609344 km/h (exact)
1 knot = 1 nautical mile per hour = 1.852 km/h (exact)
1 ft/s = 0.3048 m/s (exact)
For a quick estimate in your head: km/h × 0.62 ≈ mph, and mph × 1.6 ≈ km/h. Feet per second are almost exactly 1.5 × mph (88 ft/s is exactly 60 mph).
Worked examples
60 mph in km/h
60 × 1.609344
96.56064 km/h
100 km/h in mph
100 ÷ 1.609344
62.1371 mph
10 m/s in km/h
10 × 3.6
36 km/h
30 knots in mph
30 × 1.852 ÷ 1.609344
34.5234 mph
88 ft/s in mph
88 × 0.3048 ÷ 0.44704
60 mph
How the road drawing works
The scene is drawn to a fixed scale that is printed on it (for example 1 m = 16 px). The lane dashes follow the US standard for broken lines, 10-foot segments with 30-foot gaps, and posts stand every 10 meters. They move past the car at the speed you entered, so 60 mph really looks twice as fast as 30 mph. Past about 1,500 pixels per second the motion would turn into a blur, so the scene is slowed by a power of ten and says so on screen. The car is about 4.5 m long, at the same scale. The motion respects your device’s reduced-motion setting and pauses when the drawing scrolls out of view.
Where this comes up
- Driving abroad: speed limits in km/h, a speedometer in mph.
- Running and cycling: treadmills in mph, race paces in km/h.
- Boating and flying: speeds in knots, weather reports in mph or km/h.
- Physics homework: answers in m/s from data in km/h or ft/s.
Accuracy and rounding
Results use exact factors and are rounded only for display. “Auto” shows up to 10 significant digits; the badge says Exact when nothing was rounded away. Everyday reference speeds on the page (walking, highway, airliner) are typical values, not exact ones.
Questions
How many km/h is 1 mph?
Exactly 1.609344 km/h, because a mile is exactly 1,609.344 meters.
Is 100 km/h faster than 60 mph?
Yes, slightly: 100 km/h is about 62.14 mph, and 60 mph is 96.56 km/h.
What is a knot?
One nautical mile per hour: exactly 1.852 km/h, or about 1.1508 mph. It is used at sea and in aviation.
Is the animation really to scale?
Yes. Markings move at your speed multiplied by the pixels-per-meter scale shown on the scene. Very high speeds are slowed by a stated power of ten so the motion stays visible.