Speed Distance Time Calculator
Know any two of speed, distance and time and the calculator finds the third, in whichever units you like — km/h, mph, knots, metres per second, minutes or hours. A second mode works out the true average speed of a journey with several legs. Every step is shown, and the speed result comes back in other units and as running pace. Runs in your browser; free, no sign-up.
Calculated
Results
60 km/h
Speed
2 h 30 min
Time
The working
- Convert to SI units: D = 150000 m; T = 9000 s.
- Speed = distance ÷ time.
- Speed = 150000 m ÷ 9000 s = 16.67 m/s
- In the unit you chose: 16.67 m/s = 60 km/h.
The speed in other units
| Unit | Speed |
|---|---|
| m/s | 16.67 |
| km/h | 60 |
| mph | 37.28 |
| ft/s | 54.68 |
| kn | 32.4 |
| cm/s | 1667 |
| min per km (pace) | 1:00 |
| min per mile (pace) | 1:37 |
Treats speed as constant over the journey. For a trip with changing speeds, use the several-legs mode, which gives the true average.
How to Use the Speed Distance Time Calculator
- 1. Pick what you are finding. Choose speed, distance or time. The triangle shades the quantity you are solving for.
- 2. Enter the other two. Give each a unit. For a time such as 2 h 30 min, switch the time entry to hours, minutes and seconds instead of converting by hand.
- 3. Read the answer and the working. The result appears in the unit you chose, with the conversion to SI units and the formula shown. A speed is also listed in every common unit and as pace per kilometre and per mile.
- 4. For a trip with different speeds, use the several-legs mode. Describe each leg by its distance and either its speed or its time; the calculator adds up distance and time and divides.
The Formula and the Triangle
Speed is how much distance is covered per unit of time, so speed = distance ÷ time. Rearranging gives the other two forms. The triangle is a memory aid: put distance (D) on top and speed (S) and time (T) underneath, cover the one you want, and what is left is the calculation.
| To find | Formula | Example |
|---|---|---|
| Speed | S = D ÷ T | 150 km ÷ 2.5 h = 60 km/h |
| Distance | D = S × T | 60 km/h × 2.5 h = 150 km |
| Time | T = D ÷ S | 150 km ÷ 60 km/h = 2.5 h |
The units must agree: km with hours gives km/h, but km with minutes gives km/min. The calculator converts for you.
Worked Example
A train covers 150 km in 2.5 hours (the calculator's default). Its speed is 150 ÷ 2.5 = 60 km/h. In SI units that is 16.67 m/s; it is also 37.28 mph, 32.4 knots and 54.68 ft/s. As a pace it is 1:00 per kilometre and 1:37 per mile. A marathon of 42.195 km run in 3 h 30 min is 12.06 km/h — a pace of 4:59 per kilometre or 8:01 per mile.
Average Speed Over a Trip
Average speed is total distance divided by total time. It is not the mean of the speeds, because you spend more time at the slow speed. Drive 60 km at 80 km/h and another 60 km at 40 km/h: the legs take 0.75 h and 1.5 h, so the 120 km took 2.25 h and the average is 53.33 km/h. The plain mean of 80 and 40 is 60 km/h, which overstates it. The several-legs mode uses these numbers as its default and flags the difference.
For two legs of equal distance the average speed is the harmonic mean of the two speeds, 2ab ÷ (a + b); here 2 × 80 × 40 ÷ 120 = 53.33 km/h. A rest stop is a leg with distance 0 and a time.
Useful Conversions
| Unit | In m/s | In km/h |
|---|---|---|
| 1 km/h | 0.2778 | 1 |
| 1 mph | 0.44704 (exact) | 1.609344 (exact) |
| 1 knot | 0.5144 | 1.852 (exact) |
| 1 ft/s | 0.3048 (exact) | 1.0973 |
The mile (1609.344 m), foot (0.3048 m) and nautical mile (1852 m) are exact definitions. Source: NIST Special Publication 811, Appendix B.
Common Mistakes
- Mixing units. 2 h 30 min is 2.5 h, not 2.3 h. Minutes are sixtieths, not hundredths.
- Averaging the speeds. Use total distance over total time instead.
- Confusing speed with velocity. Speed has no direction and is never negative. Average velocity is displacement over time, so a round trip has an average velocity of zero but a positive average speed.
- Assuming constant speed. The formula describes an average. For motion that speeds up or slows down at a steady rate, use the Kinematics Calculator.
Frequently Asked Questions
- How do you calculate average speed?
- Divide the total distance travelled by the total time taken, including any stops. If the speed changed, find each leg's time from its distance and speed, add the times, and divide the total distance by the total time.
- How do I find time from distance and speed?
- Divide the distance by the speed: t = d ÷ s. Keep the units consistent. 150 km at 60 km/h is 2.5 h, which is 2 h 30 min. The calculator shows the answer in hours, minutes and seconds as well.
- How do I convert km/h to m/s?
- Divide by 3.6, because 1 km is 1000 m and 1 h is 3600 s. So 36 km/h is 10 m/s. Going the other way, multiply m/s by 3.6.
- What is the difference between speed and velocity?
- Speed is how fast you move and has only a size. Velocity also has a direction, so it can be negative or zero. Average speed uses the distance travelled; average velocity uses the net displacement.
- Why is my average speed not the average of my speeds?
- Because each speed lasts for a different time. You cover the same 60 km at 80 km/h in less time than at 40 km/h, so the slower leg counts for more. The correct average weights each speed by the time spent at it.
- What is running pace?
- Pace is time per unit distance — the reciprocal of speed — usually written as minutes and seconds per kilometre or per mile. A speed of 12 km/h is a pace of 5:00 per kilometre.