How it works
One simple relationship ties together speed, distance and time: know any two and you can find the third. Use it to estimate driving time, work out your average speed, or check a physics problem. The calculator shows time as hours and minutes rather than awkward decimals — two and a half hours is 2 h 30 min, not 2.3.
speed = distance ÷ time · distance = speed × time · time = distance ÷ speed m/s = km/h ÷ 3.6 · mph = km/h × 0.6214Worked examples. Time: 450 km at an average 100 km/h takes 4.5 hours — 4 h 30 min. Speed: 300 km in 2 h 30 min is 300 ÷ 2.5 = 120 km/h (33.33 m/s, about 74.6 mph). Distance: 3 hours at 90 km/h covers 270 km. The same formulas work in miles: 180 miles at 60 mph takes 3 hours.
Watch the time units
The classic mistake is writing an hour and a half as 1.30. It is 1.5 hours, because an hour has 60 minutes, not 100. That is why hours and minutes are separate fields here. To convert by hand, minutes ÷ 60 gives the fraction of an hour: 45 min = 0.75 h, 20 min = 0.333 h.
Average speed is not the average of speeds
Drive 120 km out at 60 km/h and back at 120 km/h and your average is not 90. The outbound leg took 2 hours and the return 1 hour: 240 km in 3 hours = 80 km/h. Always divide total distance by total time.
Speed unit conversions
| From | To | Multiply by |
|---|---|---|
| km/h | m/s | 0.27778 (÷ 3.6) |
| km/h | mph | 0.62137 |
| mph | km/h | 1.60934 |
| knots | km/h | 1.852 |
Pace for runners and walkers
Runners think in minutes per kilometre rather than km/h. 12 km/h is a pace of 5:00 per km; 10 km/h is 6:00 per km. The pace line in the results converts any speed automatically; for race splits, use the dedicated pace calculator.
Real-world travel time
The result assumes a constant average speed with no stops. For road trips add time for fuel, food and traffic — a common rule of thumb is 10–15 minutes per two hours of driving. Always keep to posted speed limits.
Planning the fuel too? Use the gas trip cost calculator and the fuel economy calculator. To switch between units, try km to miles.