Miles per Hour
Calculate speed from distance and time.
About the Miles per Hour
Average speed from distance and time. This is average speed over the whole journey, not the number on your speedometer at any moment.
How to use it
- Enter the distance.
- Enter the time taken.
- Read the average speed.
The formula
Average speed is total distance divided by total time. The only real difficulty is that time is usually written in hours and minutes, and the formula needs a single decimal number.
Speed = Distance ÷ Time
Time in hours = Hours + (Minutes ÷ 60)
So 2 hours 30 minutes is 2.5 hours, and 1 hour 45 minutes is 1.75 — not 1.45. That conversion is where nearly every wrong answer comes from. The same relationship rearranges to give the other two quantities: Distance = Speed × Time and Time = Distance ÷ Speed.
Average speed is not the average of your speeds. It is total distance over total time, which weights slow sections more heavily because you spend longer in them.
Worked examples
| Distance | Time | Time in hours | Average speed |
|---|---|---|---|
| 150 miles | 2 h 30 m | 2.50 | 60.0 mph |
| 150 miles | 2 h 15 m | 2.25 | 66.7 mph |
| 26.2 miles | 3 h 45 m | 3.75 | 7.0 mph |
| 500 miles | 8 h 20 m | 8.33 | 60.0 mph |
Rows one and two show how little time a higher average actually buys. Lifting the average from 60 to 66.7 mph over 150 miles saves fifteen minutes across the whole journey. On a shorter trip the saving shrinks proportionally, which is the arithmetic behind the observation that speeding rarely gains what drivers imagine it does — especially once junctions and traffic lights are involved.
Common mistakes
- Writing 2 hours 30 minutes as 2.30. Minutes are sixtieths, not hundredths. Two and a half hours is 2.5. Entering 2.30 produces a speed roughly 8% too high, and the error is invisible because the answer still looks reasonable.
- Averaging the speeds instead of the journey. Driving 60 mph for one hour then 20 mph for one hour averages 40. Covering 60 miles at 60 then 60 miles at 20 does not — that is 120 miles in 4 hours, or 30 mph. Slow sections take more time, so they carry more weight.
- Mixing units. Distance in miles with time in minutes gives miles per minute. Convert time to hours first, or multiply the result by 60.
- Forgetting stops. Average speed for a journey includes every minute you were not moving. A trip average always looks lower than the speedometer suggested, and that gap is the stops.
Terms explained
- Average speed
- Total distance divided by total elapsed time, including stops. What this calculates.
- Instantaneous speed
- Your speed at one moment — what the speedometer shows.
- Velocity
- Speed with a direction attached. In physics the distinction matters; in everyday use the words are interchangeable.
- Pace
- Time per unit distance, the inverse of speed. Runners use minutes per mile because it is easier to hold in your head while moving.
- Elapsed time
- The full clock time from start to finish, stops included.
- Knot
- One nautical mile per hour, about 1.151 mph. Standard at sea and in aviation.
Common questions
- How do I convert minutes to a decimal?
- Divide by 60. Thirty minutes is 0.5, fifteen is 0.25, twenty is 0.333. Writing 2 hours 30 minutes as 2.30 is the most common mistake on this page.
- Why is my average speed lower than my cruising speed?
- Because average speed counts every stop, junction and slow section. A journey with a 70 mph cruise often averages in the fifties once the whole trip is included.
- How do I convert mph to km/h?
- Multiply by 1.609. So 60 mph is about 96.6 km/h. To go the other way, multiply km/h by 0.621.
- Can I average two speeds directly?
- Only if you spent equal time at each. For equal distances you need the harmonic mean, which is why 60 mph out and 20 mph back averages 30, not 40.
- How do I work out pace from speed?
- Divide 60 by your speed in mph. A 7 mph run is about 8 minutes 34 seconds per mile.
- What if my distance is in kilometres?
- The calculation is identical — you simply get kilometres per hour instead. Speed takes its units from whatever you put in.
- How long will a journey take at a given speed?
- Divide distance by speed. 500 miles at 60 mph is 8.33 hours, which is 8 hours 20 minutes — multiply the 0.33 by 60 to convert the decimal back to minutes.
- Does this work for running or cycling?
- Yes. A marathon in 3 hours 45 minutes is 26.2 miles in 3.75 hours, an average of 7.0 mph. Most runners then convert that to pace per mile.