Speed Distance Time Calculator

How to use this tool

Choose what to calculate. "Speed, distance or time" takes two of the three and finds the third: enter the distance and the speed for the time a trip takes, the distance and the time for the average speed, or the speed and the time for the distance covered. Each figure has its own unit menu, so 250 miles at 65 mph or 500 nautical miles at 20 knots works as well as kilometres, and the speed menu includes pace in minutes per kilometre or per mile for runners. "Average speed over several legs" takes up to five legs, each with a distance and either a speed or a time. "Arrival time at a pace" adds a start time and gives you the clock time you get there.

The input people most often get wrong is the time. Typed into a single box, 1.30 is not an hour and a half; it is 1.3 hours, which is 1 hour 18 minutes. This calculator avoids the trap by taking hours, minutes and seconds in separate boxes, and if you prefer a decimal you can switch to that form and choose hours, minutes, seconds or days. The second common slip is pace: 5.5 in the pace box means 5 minutes 30 seconds per kilometre, so type 5:30 or 5.5 but not 5.30, which the calculator reads as 5 minutes 18 seconds.

What the calculation is doing

Every entry is converted to metres and seconds before anything else happens. Distance is multiplied by its unit factor: 1,000 for kilometres, 1,609.344 for miles, 1,852 for nautical miles, 0.3048 for feet and 0.9144 for yards, all exact by definition and taken from NIST Special Publication 811 (the Length Converter uses the same factors). Speed goes to metres per second the same way: km/h divided by 3.6, mph multiplied by 0.44704, knots multiplied by 1,852 ÷ 3,600 and ft/s multiplied by 0.3048. Time becomes seconds. Then speed = distance ÷ time, distance = speed × time or time = distance ÷ speed, and the answer is converted back into every unit you might want, which is why the figure cards show km/h, mph, m/s, ft/s, knots and both paces at once.

Pace is the inverse of speed, time per unit of distance rather than distance per unit of time. Seconds per kilometre is 1,000 divided by the speed in m/s, so 12 km/h (3.333 m/s) is 300 s per km, or 5:00. That inversion is why a 10% faster pace is not a 10% shorter time per kilometre: pace and speed move in opposite directions and by different proportions. A knot is one nautical mile per hour, and because the nautical mile is 1,852 m, a knot is 1.852 km/h or 1.151 mph.

For several legs the average speed is the total distance divided by the total time, exactly as for one leg, and the calculator shows the plain mean of the leg speeds beside it so you can see how far out that shortcut is. Arrival time is the start time plus the travel time, wrapped past midnight with a note of how many days later you get there. Nothing here is an approximation: the only rounding is in the display, which shows three decimals for most figures and whole seconds for times.

Why 60 out and 120 back averages 80, not 90

Take a 100 km trip each way. The outward leg at 60 km/h takes 1:40:00, the return at 120 km/h takes 0:50:00, so the round trip is 200 km in 2:30:00, which is 80 km/h. The mean of the two speeds, 90 km/h, would have you home at 2:13:20, 16 minutes and 40 seconds before you actually arrive. The slow leg takes twice as long as the fast one, so it carries twice the weight in the average. For equal distances the true average is the harmonic mean, 2 × 60 × 120 ÷ (60 + 120) = 80 km/h, and for any number of equal legs it is the number of legs divided by the sum of 1 ÷ speed.

The same arithmetic sets a ceiling that surprises people. Having driven out at 60 km/h, no return speed at all can lift the average to 120 km/h, because the outward half alone used up the 1:40:00 that 120 km/h would allow for the whole 200 km. Averaging 90 needs a return at 180 km/h: 60 out and 180 back gives 90 km/h. Even a return at a million km/h only reaches 119.993 km/h. If you are behind schedule at the halfway point, the speed needed to recover rises far faster than intuition suggests, and past a certain point it cannot be done.

The plain mean of the speeds is right only when the legs take equal time, not equal distance, because time is what an average speed is weighted by. With unequal distances the average is the sum of the distances divided by the sum of each distance over its speed, and the error can go either way. 100 km at 100 km/h followed by 10 km through a town at 50 km/h is 110 km in 1:12:00, an average of 91.667 km/h; here the mean of the speeds, 75 km/h, is too low, because the fast leg dominates the time. Runners meet the same trap with paces: an average pace is total time over total distance, and the mean of the split paces only matches it when every split is the same length.

Time to cover common distances

Each cell is the moving time at a steady speed, as h:mm:ss. Read across a row to see how little the higher speeds buy: 100 km takes 5:00:00 at 20 km/h and 3:20:00 at 30 km/h, but 1:00:00 at 100 km/h against 0:50:00 at 120 km/h, because time falls with the inverse of speed rather than in a straight line.

A worked example you can check on paper

The calculator opens with 100 km at 80 km/h. Distance: 100 × 1,000 = 100,000 m. Speed: 80 ÷ 3.6 = 22.222 m/s. Time: 100,000 ÷ 22.222 = 4,500 s, and 4,500 ÷ 3,600 = 1.25 hours, which is 1:15:00. The cross check in the other unit system: 80 km/h ÷ 1.609344 = 49.71 mph, and 49.71 mph for 1.25 hours covers 62.137 miles, which is 100 km again. The table of other speeds under the result is the same sum repeated for walking, cycling and driving speeds.

Two figures in the result box are worth checking too. Going 10% faster, at 88 km/h, takes 1:08:11 and saves 6 minutes and 49 seconds. Going 10% slower, at 72 km/h, takes 1:23:20 and costs 8 minutes and 20 seconds. The same percentage costs more than it saves, which is the inverse relationship again: the time at 88 km/h is 1 ÷ 1.1 of the original, but the time at 72 km/h is 1 ÷ 0.9 of it.

Mistakes that catch people out

Averaging the speeds. Two legs at 60 and 120 km/h do not average 90. Total distance over total time is the only average that predicts when you arrive; use the legs mode and it does the weighting for you.

Typing 1.30 for an hour and a half. As a decimal, 1.30 hours is 1 hour 18 minutes and 1.5 hours is the figure you meant. Use the hours, minutes and seconds boxes, or switch to the decimal form and choose minutes so that 90 means 90 minutes.

Writing pace with a decimal point. 5.30 in the pace box is 5.3 minutes, or 5:18 per km. Type the colon form, 5:30, unless you mean decimal minutes.

Mixing knots, mph and km/h. A knot is a nautical mile per hour and a nautical mile is 1,852 m, so 20 knots is 37.04 km/h or 23.016 mph. Pick nautical miles and knots together for sea and air; the calculator converts between all three, but the unit menus have to match what you typed.

Using the cruising speed as the average. The time here is the moving time at a steady speed. Towns, junctions, fuel stops and a slow start all sit outside it, and a door to door average is always lower than the speed on the open road. Take the distance and total time from a trip you have already made to find the average you really hold, then plan with that.

Popular calculations

Each address opens the calculator with those figures filled in, and everything can be changed once it is open.

Time to cover a distance

Average speed from distance and time

Distance covered at a speed

Average speed over several legs

Arrival time from a start time

How this was checked

The unit factors were compared with NIST Special Publication 811, Appendix B.9, which marks the exact ones in bold: the engine reproduces the foot, yard, mile, nautical mile, ft/s and mi/h rows to the last digit and the rounded km/h and knot rows to the seven significant figures NIST prints. The survey mile was checked against the NIST survey foot page at 1,609.347218694 m, 3.2 mm longer than the international mile. The marathon distance of 26 miles 385 yards from World Athletics comes out at 42,194.988 m from the mile and yard factors together, which rounds to the 42.195 km the calculator uses.

The engine was then tested against independent routes in a Node script kept with the build. 20,000 random values were converted through every distance, speed and time unit and back with a worst relative error of 2.2 × 10⁻¹⁶, and 20,000 random distance and speed pairs were solved for time, then back to speed and distance, to the same precision. Stepping forward one second at a time at 80 km/h reaches 100 km after 4,500 steps, the engine's 1:15:00. For the legs mode, 5,000 random sets of one to five legs matched the distance weighted harmonic mean exactly, 5,000 equal distance sets matched the plain harmonic mean to 4.4 × 10⁻¹⁶, and the arithmetic mean of the speeds was never below the true average. The OpenStax College Physics example of a 6 km round trip in 30 minutes returned its 12 km/h, and clock arithmetic was checked across midnight and over the 16 day Moon trip. Every address in the lists above was opened and checked for a distinct title, the right answer and clean exports at desktop, tablet and phone widths.

Common questions

How do you calculate speed, distance and time?

Speed is distance divided by time, distance is speed multiplied by time, and time is distance divided by speed. The only care needed is with units: 100 km in 1 hour 15 minutes is 100 ÷ 1.25 = 80 km/h, not 100 ÷ 1.15. The calculator converts everything to metres and seconds first, so you can mix miles, knots and minutes per kilometre without doing the conversions yourself.

How do you convert km/h to mph?

Divide by 1.609344, because a mile is exactly 1,609.344 metres. 100 km/h is 62.137 mph and 80 km/h is 49.71 mph. Going the other way, multiply: 65 mph is 104.607 km/h. For metres per second, divide km/h by 3.6, so 80 km/h is 22.222 m/s. A knot is one nautical mile of 1,852 m per hour, which makes 20 knots 37.04 km/h or 23.016 mph.

How do you work out average speed over several legs?

Add up the distances, add up the times, and divide the total distance by the total time. Do not average the speeds of the legs. Driving 100 km at 60 km/h and 100 km back at 120 km/h takes 1:40:00 plus 0:50:00, which is 200 km in 2:30:00, an average of 80 km/h. The mean of 60 and 120 is 90, and that is wrong because the slow leg takes twice as long as the fast one.

How do you convert pace to speed?

Pace in minutes per kilometre is 60 divided by the speed in km/h, and speed is 60 divided by the pace in decimal minutes. 5:00 per km is 60 ÷ 5 = 12 km/h, and 5:30 per km is 60 ÷ 5.5 = 10.909 km/h. For miles the same rule gives 8:00 per mile as 7.5 mph. A pace of 5:41 per km is 9:09 per mile, because a mile is 1.609344 km.

How do I work out my arrival time?

Divide the distance by the speed you expect to hold, then add that time to your start time. 350 km at 90 km/h takes 3:53:20, so leaving at 14:15 you arrive at 18:08. The arrival mode does this for you, carries over midnight, and shows the halfway time as well. Add your stops separately, because the speed you enter is the moving average.

Which mile does the calculator use?

The international mile of exactly 1,609.344 metres, the definition in NIST Special Publication 811. The older US survey mile is about 3.2 mm longer, a difference of 2 parts per million, and NIST asked for it to be avoided after 2022 except for historic and legacy uses. Over a 250 mile drive the two differ by 0.8 m, far below anything a speedometer or GPS can resolve.

Related Calculators and Reference

• Speed Converter: km/h, mph, knots, m/s, ft/s and Mach when you only need the unit changed.
• Pace Calculator: race splits and finish times from a target pace.
• Time Calculator: add and subtract hours, minutes and seconds, for stops and layovers on top of the moving time.
• Gas Cost Calculator: the fuel bill for the same trip once you know the distance.
• Kinetic Energy Calculator: what the speed you just worked out means in energy, which rises with its square.
• Gear Ratio and RPM to Speed Calculator: road speed from engine RPM, gear ratio and tyre size.
• Stopping Distance Calculator: reaction plus braking distance for a given speed and road surface.
• NIST SP 811 Appendix B.9: the conversion factors for length and velocity used here, with the exact ones marked.