Use distance and average speed to calculate time, turn decimal hours into minutes, and account for stops or different travel speeds.
Open the km to hours calculator · More Physics and Math videos
The calculation
Time (h) = distance (km) ÷ average speed (km/h)
Worked example
150 km at an assumed average 60 km/h takes 2.5 h, or 2 h 30 min. A separate 20-minute stop makes 2 h 50 min. Equal 60 km legs at 60 and 30 km/h take 3 hours total, giving average speed 40 km/h.
A distance alone does not determine travel time. Use an appropriate average speed and avoid adding stops twice if the average already includes them.
Video chapters
- 0:00 — Kilometers need a speed to become time
- 0:17 — Think in kilometers for each hour
- 0:37 — Divide distance by speed
- 0:59 — Decimal hours are not clock minutes
- 1:22 — Add stops only when needed
- 1:44 — Different legs need separate calculations
- 2:03 — Do not simply average the two speeds
- 2:25 — Match units and define the time window
Read the full transcript
How long does a hundred-fifty-kilometer trip take? The distance alone cannot tell us. At a higher average speed, the same route takes less time. We need a speed matched to the trip, then we can connect distance, rate, and elapsed time.
Assume the average travel speed is sixty kilometers per hour. That means sixty kilometers correspond to each hour in the model. One hour covers sixty; two hours cover one hundred twenty. Thirty kilometers remain. The clock and the distance ruler must advance together.
Divide one hundred fifty kilometers by sixty kilometers per hour. Kilometers cancel and hours remain. The answer is two point five hours. The half-hour corresponds to the last thirty kilometers, because thirty is half of sixty. Our route has two full hourly sections and half of another.
Convert the fractional hour to minutes by multiplying by sixty. Zero point five times sixty is thirty. So two point five hours means two hours and thirty minutes, not two hours and fifty minutes. Check the journey backward: sixty kilometers per hour times two point five hours returns one hundred fifty kilometers.
If sixty kilometers per hour describes travel while moving, a separate twenty-minute stop adds to the journey. Two hours thirty minutes plus twenty minutes is two hours fifty minutes. But if the average speed already includes stops across the full trip, adding them again would count that time twice.
Now consider a different route: sixty kilometers at sixty kilometers per hour, followed by sixty kilometers at thirty. The first leg takes one hour; the second takes two. Add the times to get three hours. Equal distances at different speeds do not take equal amounts of time.
That second route totals one hundred twenty kilometers over three hours, so its average speed is forty kilometers per hour. Simply averaging sixty and thirty would give forty-five, which is wrong here. The slower leg occupies more time. Average speed is total distance divided by total elapsed time.
Use distance divided by a suitable average speed, with compatible units. Convert fractional hours by multiplying by sixty, and account for stops consistently. For our original example, one hundred fifty kilometers at sixty kilometers per hour gives two hours and thirty minutes of modeled travel time.