Speed Calculator
The formula
Average speed = distance ÷ time
With distance in kilometres and time in hours, the result is in km/h. The same relationship gives the other two quantities: time = distance ÷ speed and distance = speed × time.
Worked examples
- 150 km driven in 1.5 hours: 150 ÷ 1.5 = 100 km/h.
- A marathon (42.195 km) run in 2 hours would mean an average of 21.1 km/h — roughly the pace of today's world record.
- How long for 240 km at 80 km/h? 240 ÷ 80 = 3 hours.
Watch out for minutes
The time must be in decimal hours: 1 h 30 min is 1.5, not 1.30. To convert, divide the minutes by 60:
| Time | Decimal hours |
|---|---|
| 15 min | 0.25 |
| 20 min | 0.333 |
| 45 min | 0.75 |
| 1 h 10 min | 1.167 |
| 2 h 40 min | 2.667 |
Converting units
- km/h → m/s: divide by 3.6 (100 km/h = 27.8 m/s).
- m/s → km/h: multiply by 3.6.
- km/h → mph: multiply by 0.621 (100 km/h ≈ 62 mph); mph → km/h: multiply by 1.609.
- Knots (sea and air): 1 knot = 1.852 km/h.
Average speed is not the average of speeds
If you drive 60 km at 60 km/h and then 60 km at 120 km/h, your average speed is not 90 km/h. The trip takes 1 h + 0.5 h = 1.5 h for 120 km, so the average is 80 km/h: you spend more time at the lower speed. Always divide the total distance by the total time.
Reference speeds
Walking is about 5 km/h, an easy run 9–11 km/h, city cycling 15–20 km/h. On motorways, a few km/h more saves surprisingly little time: over 100 km, driving at 130 instead of 120 km/h saves under 4 minutes, while noticeably increasing fuel consumption.
For running, the pace calculator gives minutes per kilometre; the fuel consumption calculator estimates the cost of a journey.
Frequently Asked Questions
How do I enter 1 hour 45 minutes?
As decimal hours: 1.75. Divide the minutes by 60 and add them to the hours (45 ÷ 60 = 0.75).
How do I convert km/h to m/s?
Divide by 3.6. For example, 90 km/h = 25 m/s.
How do I calculate travel time?
Divide the distance by the speed: 300 km at 100 km/h takes 3 hours. Add breaks and traffic for a realistic estimate.