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Speed Calculator — How Fast Were You Going?

By Sofia Andersen · Last updated 15 October 2026

How fast was I actually going? Distance divided by time. That is all this page needs from you: how far you went and how long it took, and it gives back your average speed in mph or km/h, plus pace if you were running.

Enter your numbers

Result

Average is the number that gets you home

Speed = Distance ÷ Time. Everything else is unit conversion. To go from mph to km/h, multiply by 1.609. To go the other way, divide by 1.609. Pace is the same idea flipped over: Pace = Time ÷ Distance.

One thing worth saying plainly: this is average speed. A car that averages 64 mph was doing 75 on the open road and 20 in town. The average is what matters for arrival times, which is why the calculator gives you that and not a top speed.

A drive. 240 miles in 3 hours 45 minutes. First turn the time into hours: 3 h 45 min = 3.75 hours. Then 240 ÷ 3.75 = 64 mph. In metric, 240 miles is 386 km, and 386 ÷ 3.75 = 103 km/h. If you are planning a drive, work with the average, not the speed limit. Traffic, fuel stops, and town stretches drag the average well below the fastest part of the journey. A 240-mile trip at a true 64 mph average takes 3 h 45 min, but most drivers plan on 4 hours or more.

Two more, checked by hand

A shorter trip. 100 km in 1 hour 20 minutes. 1 h 20 min = 1.333 hours. 100 ÷ 1.333 = 75 km/h, which is about 46.6 mph.

A run. 10 km in 52 minutes. Pace = 52 ÷ 10 = 5.2 minutes per kilometre, in other words 5 min 12 sec per km. As a speed, that is 10 ÷ (52 ÷ 60) = 11.5 km/h. For runners, pace is usually the more useful number: it tells you what each mile or kilometre felt like, and it is how training plans are written. Cyclists tend to live in km/h or mph, runners in pace. The calculator shows both so you can use whichever your plan uses. The answer shows in both mph and km/h anyway.

The traps

  • Mixing units, miles with km/h, is the classic slip. Check the unit labels before trusting the answer.
  • Forgetting that a “3 hour 45 minute” trip is 3.75 hours, not 3.45. The calculator handles this; mental maths often does not.
  • Treating average speed as the speed you drove the whole way. It is not. It is the whole trip smoothed out.

Questions

How do you calculate speed?

Divide distance by time, in matching units. Miles divided by hours gives mph; kilometres divided by hours gives km/h.

How do I convert mph to km/h?

Multiply mph by 1.609. So 64 mph is about 103 km/h. Divide km/h by 1.609 to go back.

What is the difference between speed and pace?

Speed is distance per unit of time (how far in an hour). Pace is time per unit of distance (how long each mile took). Runners use pace; drivers use speed. They are two views of the same trip.

Why does my trip take longer than distance ÷ speed limit?

Because your average speed is lower than the fastest stretch. Town traffic, junctions, and stops all pull the average down, so the real trip time is longer than the speed-limit maths suggests.

How do I work out my running pace?

Divide the time by the distance. A 10 km run in 52 minutes is 5.2 minutes per kilometre, which is 5 min 12 sec per km.

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