Quick Reference
Speed Reference Table
Common speeds in all four units for quick reference:
| Context | mph | km/h | m/s |
|---|---|---|---|
| Leisurely walk | ~2.5 | ~4 | ~1.1 |
| Brisk walk | ~3.5 | ~5.6 | ~1.6 |
| Running (average) | ~6 | ~9.7 | ~2.7 |
| Competitive 5K pace | ~9 | ~14.5 | ~4 |
| Cycling (casual) | ~12 | ~19 | ~5.4 |
| City driving | ~30 | ~48 | ~13.4 |
| Highway driving | ~65 | ~105 | ~29 |
| Cheetah (top speed) | ~75 | ~121 | ~33.5 |
| High-speed rail | ~200 | ~320 | ~89 |
| Commercial aircraft | ~575 | ~925 | ~257 |
| Speed of sound (sea level) | ~767 | ~1,235 | ~343 |
Mental Math Shortcuts
For quick mental conversions without a calculator:
- mph → km/h: Multiply by 1.6 (close enough for most purposes). 50 mph × 1.6 = 80 km/h.
- km/h → mph: Multiply by 0.6 (or divide by 1.6). 100 km/h × 0.6 = 60 mph.
- km/h → m/s: Divide by 3.6. 90 km/h ÷ 3.6 = 25 m/s.
- m/s → km/h: Multiply by 3.6. 10 m/s × 3.6 = 36 km/h.
- mph → knots: Multiply by 0.87. 100 mph × 0.87 ≈ 87 kn.
Why Different Systems Use Different Units
Speed units evolved separately in different contexts, which is why we have so many:
- Miles per hour (mph) — used in the US and UK for road speeds, derived from the statute mile defined in 1593.
- Kilometers per hour (km/h) — the metric standard used in most countries worldwide for road and rail transport.
- Meters per second (m/s) — the SI unit of speed, used in physics and engineering because it integrates cleanly with other SI units.
- Knots — historically derived from the nautical practice of measuring a ship's speed by counting how many knots in a rope passed through a sailor's hand in 30 seconds. Still used in aviation and maritime navigation worldwide because nautical miles align with degrees of latitude.
Frequently Asked Questions
How do I convert mph to km/h?
Multiply by 1.60934. A quick mental approximation: multiply by 1.6 (or by 8 and divide by 5). So 60 mph × 1.6 ≈ 96 km/h.
What is a knot?
A knot is one nautical mile per hour. One nautical mile is 1,852 meters (slightly longer than a statute mile). Knots are used in aviation and maritime navigation.
How fast is Mach 1?
Mach 1 is the speed of sound, approximately 343 m/s (767 mph / 1,235 km/h) at sea level and 20°C. The speed of sound decreases at higher altitudes where the air is colder and less dense.
What speed unit do scientists use?
Scientists typically use meters per second (m/s), the SI base unit for speed. Miles per hour and kilometers per hour are more common in everyday and transport contexts.
How do I convert km/h to m/s?
Divide by 3.6. For example, 90 km/h ÷ 3.6 = 25 m/s. To convert back, multiply by 3.6.