In this article
Speed, distance and time are three views of the same thing: how far you go, how long it takes, and how fast you move. Know any two and you can find the third. The formulas are short, but the units and the idea of average speed trip people up, especially when a journey is made at different speeds.
The three formulas
- 1Write down what you knowDistance = 150 km, speed = 60 km/h.
- 2Choose the formulaTime = distance ÷ speed.
- 3Divide150 ÷ 60 = **2.5 hours**.
- 4Convert to hours and minutes0.5 hour is 30 minutes, so the trip takes **2 h 30 min**.
Choose what to find, fill in the other two values and press Solve. The tool shows time in hours and minutes as well as decimal hours.
Keep the units matching
The tool uses kilometres, hours and km/h. If your numbers are in other units, convert first. Minutes must become hours: 90 minutes is 1.5 hours, not 90. Metres must become kilometres: 2,500 m is 2.5 km. Mixing km with minutes is the most common reason an answer is off by a factor of 60.
- km/h to m/s: divide by 3.6. m/s to km/h: multiply by 3.6.
- Minutes to hours: divide by 60. Hours to minutes: multiply by 60.
- Metres to km: divide by 1,000.
Travel time at different speeds
| Speed | Time for 150 km | Speed in metres per second |
|---|---|---|
| 40 km/h | 3 h 45 min | 11.11 m/s |
| 50 km/h | 3 h 0 min | 13.89 m/s |
| 60 km/h | 2 h 30 min | 16.67 m/s |
| 75 km/h | 2 h 0 min | 20.83 m/s |
| 90 km/h | 1 h 40 min | 25.00 m/s |
The same 150 km. Doubling the speed halves the time, but going from 40 to 60 km/h saves more minutes than going from 75 to 90.
Extra speed gives smaller and smaller savings. Going from 40 to 60 km/h saves 75 minutes here, while going from 75 to 90 km/h saves only 20.
Average speed is not a simple average
Suppose you drive 60 km to a town at 60 km/h and return at 40 km/h. The simple average of the two speeds is 50, but the real average speed is total distance ÷ total time. The way there takes 1 hour and the way back takes 1.5 hours. The total is 120 km in 2.5 hours, which is 48 km/h. You spend longer at the slower speed, so it pulls the average down.
- (60 + 40) ÷ 2
- Ignores the time spent at each speed
- Would give 2 h 24 min for 120 km
- 120 km ÷ 2.5 h
- Counts the longer time at 40 km/h
- Gives 2 h 30 min for 120 km
Always add the distances and add the times first, then divide.
Solving each case
- Decide what is missing: speed, distance or time.
- Check the units and convert minutes, metres or m/s first.
- Use the matching formula or choose that option in the calculator.
- For a journey in parts, work out distance and time for each part, add them up, then find the average speed.
- Add a buffer for stops and traffic when you plan the real trip.
Questions people ask
How do I calculate travel time?
Divide the distance by the speed. For 150 km at 60 km/h, the time is 150 ÷ 60 = 2.5 hours, which is 2 hours 30 minutes.
How do I calculate speed from distance and time?
Divide the distance by the time in hours. A 90 km trip in 1.5 hours means a speed of 60 km/h.
How do I convert km/h to m/s?
Divide by 3.6. Sixty km/h is 60 ÷ 3.6 = 16.67 metres per second. To go back, multiply metres per second by 3.6.
What is average speed?
Average speed is total distance divided by total time. It is not the average of the speeds, unless you spend equal time at each speed.
Why is the average of 60 and 40 km/h not 50?
Because over equal distances you spend more time at the slower speed. The trip takes 1 hour plus 1.5 hours, so 120 km in 2.5 hours is an average of 48 km/h.
Does the calculator work for miles?
The fields are in km, km/h and hours. For miles and mph the formulas are the same, so enter the numbers in miles and mph and read the answer as miles and mph. The metres-per-second line would then not apply. The Speed Converter changes between units.