The travel triangle
Speed, distance and time are locked together: speed is how far you go in a given time. Know any two and the third follows, for planning a drive, checking a train timetable, pacing a bike ride or answering a physics question.
This speed, distance and time calculator finds whichever one you need, in miles, kilometres or metres and in mph, km/h or m/s, and converts the answer into the other units too.
How to use it
- Choose what you want to find: speed, distance or time.
- Enter the two values you know and pick their units.
- Enter time as hours, minutes and seconds.
- Read the answer, with speed, distance and time also shown in the other units.
The formulas
speed = distance ÷ time
distance = speed × time
time = distance ÷ speed
1 mph = 1.609344 km/h = 0.44704 m/s exactlyDraw a triangle with distance on top and speed and time below it. Cover the one you want: distance alone shows speed × time, and speed shows distance over time. The answer is an average; real trips speed up and slow down along the way.
Worked example: 150 miles in 2 hours 30 minutes
- Time in hours: 2 hours 30 minutes = 2.5 hours
- Speed: 150 ÷ 2.5 = 60 mph
- In other units: 96.56 km/h, or 26.82 m/s
- Distance in km: 241.4 km
The average speed is 60 mph, which is 96.56 km/h. Running it the other way, 241.4 km at 96.56 km/h also takes 2 hours 30 minutes.
Travel time at common speeds
| Speed | 100 miles takes | 100 km takes |
|---|---|---|
| 30 mph (48.28 km/h) | 3:20:00 | 2:04:16 |
| 50 mph (80.47 km/h) | 2:00:00 | 1:14:34 |
| 60 mph (96.56 km/h) | 1:40:00 | 1:02:08 |
| 70 mph (112.65 km/h) | 1:25:43 | 0:53:16 |
Going from 60 to 70 mph saves about 14 minutes over 100 miles, less than many people expect, and uses noticeably more fuel. The gas mileage calculator shows what a trip costs.
Average speed over several legs
When a trip has parts at different speeds, do not average the speeds. Add up the total distance and the total time, then divide. Drive 60 miles at 60 mph (1 hour) and another 60 miles at 30 mph (2 hours), and the average is 120 miles in 3 hours, or 40 mph, not the 45 mph a simple average of the two speeds would suggest. The slower leg takes longer, so it counts for more. The same rule applies to any trip with stops: include the stopped time in the total.
Watch the units
- Minutes are not decimals: 1 hour 30 minutes is 1.5 hours, not 1.3.
- Match the units: miles with mph, kilometres with km/h, metres with m/s.
- For running and walking, pace per mile or km is easier to use; see the running pace calculator.
- For converting speeds alone, use the unit converter.
Frequently asked questions
How do I calculate speed?
Divide the distance by the time. If you drive 120 miles in 2 hours, your average speed is 60 mph. Turn minutes into hours first: 45 minutes is 0.75 hours, so 30 miles in 45 minutes is 40 mph. Choose Speed above and enter both values.
How do I calculate travel time?
Divide the distance by the speed. A 210 mile drive at 60 mph takes 3.5 hours, which is 3 hours and 30 minutes. Remember to allow for stops and traffic, since the formula gives the time at a steady average speed. Choose Time above for hours, minutes and seconds.
How do I convert mph to km/h?
Multiply by 1.609344, because a mile is exactly 1.609344 kilometres. So 60 mph is 96.56 km/h, and 70 mph is 112.65 km/h. To go from km/h to mph, divide by 1.609344. The calculator shows every speed in mph, km/h and m/s.
What is the difference between speed and velocity?
Speed is how fast something moves, regardless of direction. Velocity is speed in a particular direction, so a car driving round a roundabout at a steady speed has a changing velocity. For trip planning, speed is what matters, and it is what this calculator works out.
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