Speed, distance and time calculator

Find speed, distance or time in one step

Speed, distance and time are tied together: know two of them and you can find the third. This calculator does the sum and shows the working, conversions included: handy for revising the speed formula, planning a road trip or checking a cycling average. It starts in miles and mph; kilometres are one click away.

How to use it

1. Under "Find the", choose "Speed", "Distance" or "Time". Its box turns green; its unit menu sets the unit of the answer.
2. Fill in the other two. Speed can be in mph, km/h, m/s, knots or min/km; distance in miles, km, m or nautical miles. Type the time in hours, minutes and seconds, or in the "or decimal hours" box.
3. The answer appears with other units, and the "Working" list shows each conversion and the formula used.
4. If you like, add a "Departure time (optional)" and tick "Add breaks" to get the total trip time and your arrival time.

The three formulas, with exact examples

• Speed: s = d ÷ t. A car covers 150 miles in 2 h 30 min. First write the time in hours: 2 h 30 = 2.5 h. Then 150 ÷ 2.5 = 60 mph.
• Distance: d = s × t. A coach travels at 45 mph for 2 h 20 min. 2 h 20 = 2 + 20 ÷ 60 h, which is 7/3 h. Distance: 45 × 7/3 = 105 miles.
• Time: t = d ÷ s. 175 miles at 70 mph: 175 ÷ 70 = 2.5 h, so 2 h 30 min.

The formula triangle on screen helps you remember all three: d at the top, s and t at the bottom. Cover the letter you want and the formula is what is left.

Golden rule: the units must match. Miles and hours give mph, metres and seconds give m/s; otherwise, convert first.

Conversions: km/h and m/s, decimal hours and minutes

1 km/h is 1,000 m in 3,600 s, so to turn km/h into m/s you divide by 3.6, and to go back you multiply by 3.6. Example: a sprinter runs 100 m in 9.58 s. Speed = 100 ÷ 9.58 ≈ 10.44 m/s, which is 10.44 × 3.6 ≈ 37.58 km/h, or about 23.35 mph. One mph is 1.609344 km/h, and one knot is 1.852 km/h, so a boat doing 20 knots moves at 37.04 km/h.

The classic mistake is with decimal hours. An hour has 60 minutes, not 100. So 1.5 h = 1 h 30 min, not 1 h 50. Likewise 1.75 h = 1 h + 0.75 × 60 min = 1 h 45 min, and 0.2 h = 12 min. The "Conversions" tab does it both ways.

Average speed over several legs: the averaging trap

You drive 60 miles out at 60 mph and 60 miles back at 40 mph. Averaging the speeds gives 50 mph, but that is wrong. The way out takes 1 h, the way back 1.5 h: 120 miles in 2.5 h is an average speed of 48 mph. You spend longer at 40 mph, which pulls the average down.

The "Several legs" tab does this for as many legs as you need: on each row, fill in two values out of distance, speed and time. The "Example: out at 60 mph, back at 40 mph" button loads the case above. Put 30 in "Total breaks (min)" and tick "Include breaks in the average speed": 120 miles in 3 h brings the average down to 40 mph.

Real journey times

On real roads your average stays well below the limit (junctions, roadworks, traffic): on a motorway, 55 to 60 mph is more realistic than 70. Road safety advice is to take a break of at least 15 minutes every two hours. For 240 miles at a 60 mph average, that is 4 h of driving plus a 20-minute stop halfway: 4 h 20 in total. With a departure time, the calculator handles midnight: leave at 10:30 PM for a 3 h 15 trip and you arrive at 1:45 AM the next day.

Frequently asked questions

How do I calculate average speed in mph?

Divide the distance in miles by the time in hours. Turn minutes into hours first: 45 min = 0.75 h. So 42 miles in 45 minutes is 42 ÷ 0.75 = 56 mph.

How do I work out travel time from distance and speed?

Divide the distance by the speed: 90 miles at 60 mph is 1.5 h, which is 1 h 30 min, not 1 h 50.

Why divide by 3.6 to get metres per second?

Because a kilometre is 1,000 metres and an hour is 3,600 seconds: 1,000 ÷ 3,600 = 1 ÷ 3.6. So 72 km/h is exactly 20 m/s.

Are my values saved?

Yes, your last values stay saved in your browser on this device. The "Clear all" button resets the calculator.