The Speed-Distance-Time Triangle
These three quantities are related by a single equation that forms the basis of all motion calculations in physics and everyday life:
- Speed = Distance ÷ Time
- Distance = Speed × Time
- Time = Distance ÷ Speed
The classic memory aid is the "SDT triangle": cover the quantity you want to find, and the remaining two show you the operation. Cover Speed → Distance over Time. Cover Distance → Speed × Time. Cover Time → Distance over Speed.
Common Speed References
| Object / Activity | Speed (km/h) | Speed (mph) | Speed (m/s) |
|---|---|---|---|
| Walking | 5 | 3.1 | 1.4 |
| Running | 12 | 7.5 | 3.3 |
| Cycling | 25 | 15.5 | 6.9 |
| City driving | 50 | 31 | 13.9 |
| Highway driving | 120 | 75 | 33.3 |
| Commercial airplane | 900 | 560 | 250 |
| Speed of sound | 1,235 | 767 | 343 |
| Speed of light | 1,080,000,000 | 670,616,629 | 299,792,458 |
Unit Conversions
This calculator works with any consistent units. If you enter distance in km and time in hours, you get speed in km/h. If you enter meters and seconds, you get m/s. To convert between common speed units:
- km/h to m/s: multiply by ÷ 3.6
- m/s to km/h: multiply by × 3.6
- mph to km/h: multiply by × 1.60934
- km/h to mph: multiply by ÷ 1.60934
Real-World Examples
- Road trip: Driving 600 km at 100 km/h takes 6 hours
- Marathon: 42.195 km in 4 hours = 10.55 km/h average speed
- Train: A bullet train covering 500 km in 2 hours travels at 250 km/h
- Sailing: Covering 150 nautical miles in 10 hours = 15 knots