Because a mile is exactly 1.609344 km, 1 mph = 1.609344 km/h exactly, and 1 km/h is about 0.621371 mph. So 65 mph is 104.6 km/h and 100 km/h is 62.14 mph. A knot is one nautical mile (1,852 m) per hour, about 1.15078 mph, and 1 m/s is exactly 3.6 km/h.
The converter uses NIST's exact factors (1 mph = 0.44704 m/s; 1 knot ≈ 0.5144444 m/s) and shows the result in all five units.
How to use the speed converter
- Enter the speed.
- Choose the unit you have and the unit you want.
- Read the result and the full table.
Formula
Worked example
Convert 65 mph to km/h and 20 knots to mph.
- 65 × 1.609344 = 104.61 km/h.
- 20 kn × 0.5144444 m/s = 10.2889 m/s ÷ 0.44704 = 23.02 mph.
- 10 m/s × 3.6 = 36 km/h.
Common speed limits converted
| mph | km/h |
|---|---|
| 25 | 40.2 |
| 35 | 56.3 |
| 55 | 88.5 |
| 65 | 104.6 |
| 70 | 112.7 |
| 75 | 120.7 |
For running and walking, minutes per mile or per kilometer is more useful than speed; the pace calculator converts between them. To estimate trip time, distance ÷ speed gives hours.
Mental shortcuts
For quick estimates without a calculator:
- mph → km/h: multiply by 1.6 (the exact factor is 1.609344, so the shortcut is about 0.6% low). 50 mph ≈ 80 km/h.
- km/h → mph: multiply by 0.6, or multiply by 5 and divide by 8. 80 km/h ≈ 50 mph.
- m/s → km/h: multiply by 3.6 (exact). 25 m/s = 90 km/h.
- knots → mph: add about 15%. 30 knots ≈ 34.5 mph.
- mph → ft/s: multiply by about 1.467 (exactly 5,280 ÷ 3,600). 60 mph = 88 ft/s.
The last one is handy for stopping and reaction distances: at 60 mph a car covers 88 feet every second, so if it takes you 1.5 seconds to react, the car travels 132 feet before you even start braking.
Speed, distance and time
Speed links distance and time: speed = distance ÷ time, so time = distance ÷ speed and distance = speed × time. Keep the units consistent: miles with hours for mph, kilometers with hours for km/h, meters with seconds for m/s.
Example: a 180-mile drive at an average of 60 mph takes 3 hours; at 70 mph it takes 2.57 hours (2 h 34 min), saving about 26 minutes. Averages on real trips are lower than cruising speed because of stops, traffic and slower roads.
For runners, pace (minutes per mile or per kilometer) is speed turned upside down: pace = 60 ÷ speed. A speed of 6 mph is a 10:00-per-mile pace; 12 km/h is a 5:00-per-km pace. Use the pace calculator for race times and splits.
Caveats and assumptions
- Display limited to 10 significant digits.
- Knots use the international nautical mile (1,852 m).
Frequently asked questions
How do I convert mph to km/h?
Multiply by 1.609344. 60 mph = 96.56 km/h.
How do I convert km/h to mph?
Divide by 1.609344 (or multiply by about 0.621371). 100 km/h = 62.14 mph.
How fast is a knot?
One nautical mile per hour: 1.852 km/h, about 1.151 mph or 0.514 m/s.
How do I convert m/s to km/h?
Multiply by 3.6. 10 m/s = 36 km/h.
What is 100 km/h in mph?
62.14 mph (100 ÷ 1.609344).
What is 60 mph in feet per second?
88 ft/s exactly (60 × 5,280 ÷ 3,600).
Is a knot faster than a mile per hour?
Yes. A knot is one nautical mile (1,852 m) per hour, about 1.15 mph, because a nautical mile is longer than a statute mile.
What is 70 mph in km/h?
112.65 km/h (70 × 1.609344).
Sources
- NIST SP 811 Appendix B.9 — Conversion factors — mile per hour, knot, foot per second and kilometer per hour factors
- NIST — SI Units: Length — inch, foot and mile definitions
This calculator gives estimates for planning and education. Check measurements, local codes, supplier specs and your school's official policy before relying on a result. See our disclaimer and how we build and check calculators.