What is a speed, distance and time calculator?
Speed, distance and time are one equation seen from three sides. Give this page any two and it gives you the third, in whatever units you happen to have. 250 miles at 90 km/h is a perfectly good question here.
The answer also shows in every speed unit at once, because the follow-up question is nearly always "and what's that in mph?".
The formulas
The units have to agree, which is where hand calculations usually go wrong. Kilometres with km/h gives hours. Metres with m/s gives seconds. Mix kilometres with metres per second and you get a number that means nothing. This page converts everything internally so you can't make that mistake.
| To find | Formula | Example |
|---|---|---|
| Speed | distance ÷ time | 120 km ÷ 1.5 h = 80 km/h |
| Distance | speed × time | 80 km/h × 1.5 h = 120 km |
| Time | distance ÷ speed | 120 km ÷ 80 km/h = 1.5 h |
Average speed isn't the average of your speeds
This catches almost everyone, and it changes how you plan a journey.
Drive 60 km at 30 km/h, then 60 km at 60 km/h. The average of 30 and 60 is 45, but that's not your average speed. The first half takes 2 hours and the second takes 1. You covered 120 km in 3 hours, so you averaged 40 km/h.
The slow section dominates because you spend longer in it. That's why shaving time off the slow part of a journey saves far more than going faster on the fast part, and why a traffic jam ruins an average that a motorway can't rescue.
Why is my real journey slower?
The arithmetic here is exact. Real journeys aren't, and the gap is almost always in the same places:
- Stops. Fuel, food, everything else. Add them separately, because they don't belong in an average speed.
- The first and last mile. Urban approaches at both ends run far below the motorway speed that dominates the middle.
- Traffic. A 400 km motorway run averages maybe 100 km/h in practice, not the 130 on the signs.
- Hills, on foot or by bike. Naismith's rule adds an hour per 600 m of ascent to a walking estimate, and it's a decent starting point.
- Your own pace. Most people overestimate how fast they walk and cycle. Measure it once with the tools here and plan from the real number.
Realistic averages
| Journey | Sign speed | Realistic average |
|---|---|---|
| City driving | 50 km/h | 20 to 25 km/h |
| Motorway, clear | 130 km/h | 110 km/h |
| Mixed long drive | 80 to 90 km/h | |
| City cycling | 15 to 18 km/h | |
| Road cycling | 25 to 30 km/h | |
| Walking, flat | 5 km/h | |
| Hill walking | 3 to 4 km/h | |
| Intercity train | 200 km/h | 120 to 140 km/h |
| Short-haul flight | 850 km/h | 500 km/h door to door |
A worked example
You've got 480 km to cover and want to arrive in 5 hours 30. What average does that need?
480 ÷ 5.5 = 87.3 km/h. Sounds easy against a 130 km/h limit. Then subtract a 30 minute stop, which leaves 5 hours and pushes it to 96 km/h, and account for the urban bits at each end. The margin disappears fast, which is exactly why departure times slip.
Measuring instead of estimating
If you want your real average over a route rather than a planned one, the GPS speedometer records distance, elapsed time, moving time and average as you go. Comparing what you planned against what happened is the quickest way to get better at planning.
Frequently asked questions
How do I calculate travel time?
Divide the distance by your average speed. 300 km at 90 km/h takes 3 hours 20 minutes. Add stops separately.
What is the formula for average speed?
Total distance divided by total time. Not the average of the individual speeds, which differs whenever the sections take different lengths of time.
Why is my real journey slower than the calculation?
Stops, traffic and the urban sections at each end. The calculation is exact. It just answers a simpler question than the road does.
Can I mix units?
Yes. Enter distance in miles and speed in km/h if that's what you have. Everything is converted internally.
Why does driving faster save so little time?
Time saved falls off sharply as speed rises. Going from 100 to 130 km/h over 300 km saves about 41 minutes. Going from 130 to 160 saves only another 26, at a big cost in fuel and risk.