Speed Calculator
Enter any two of the three variables, speed, distance, and time, and this calculator solves for the third. Switch between solving for speed, distance, or time using the mode selector. Distance supports kilometres, miles, metres, feet, and nautical miles; time is entered in hours, minutes, and seconds; speed results appear in km/h, mph, m/s, knots, and ft/s all at once.
Formula
Worked example
100 km in 1 h 30 min (5400 s): 100,000 m / 5400 s = 18.519 m/s = 66.67 km/h = 41.42 mph = 36.00 knots.
How the speed-distance-time triangle works
The relationship between speed, distance, and time is one of the most fundamental in physics: distance equals speed multiplied by time (d = v x t). Rearranging, speed equals distance divided by time, and time equals distance divided by speed. Given any two of the three values, the third is determined exactly. This calculator accepts all three solve-for modes in a single interface: pick what you want to find, enter the other two values, and the result updates instantly. Time is entered as hours, minutes, and seconds separately so you can work directly with a stopwatch reading or a journey log without converting to decimal hours by hand.
Unit conversions explained
Speed units are related by fixed, exact conversion factors defined in international standards. One mile per hour equals exactly 1.609344 kilometres per hour, because the international mile is defined as 1,609.344 metres. One metre per second equals 3.6 km/h (one km is 1,000 m; one hour is 3,600 s). A knot is one nautical mile per hour, and one nautical mile is exactly 1,852 metres, making 1 knot equal to 1.852 km/h or about 0.514 m/s. One foot per second is 0.3048 m/s, because the international foot is exactly 0.3048 metres. This calculator converts through m/s as a common base so every output is exact to the precision displayed.
Solving for distance and time
When you switch to "solve for distance", you enter a speed and a duration; the calculator multiplies them. A car at 100 km/h for 2 hours 30 minutes covers exactly 250 km. When you switch to "solve for time", you enter a speed and a distance; the calculator divides and shows the result as hours-minutes-seconds so you can read it at a glance. A 500 km trip at 90 km/h takes 5 hours 33 minutes 20 seconds, for example. Both modes support the same full range of speed units (km/h, mph, m/s, knots, ft/s) and distance units (km, mi, m, ft, nmi).
Average speed versus instantaneous speed
Every result from this calculator is average speed over the full trip, not the speed at any single moment. A car that sits in traffic for 30 minutes and then drives at 120 km/h for 30 minutes over a total of 60 km has an average speed of 60 km/h, not 120 km/h. Instantaneous speed is what a speedometer shows and what physics defines as the limit of distance over time as the time interval approaches zero. For most everyday purposes, average speed is the practical number: it tells you how long a journey will take or how far you can travel in a given time.
Real-world speed reference
| Activity / Vehicle | km/h | mph | m/s | knots |
|---|---|---|---|---|
| Casual walking | 4-5 | 2.5-3.1 | 1.1-1.4 | 2.2-2.7 |
| Brisk walking | 6-8 | 3.7-5.0 | 1.7-2.2 | 3.2-4.3 |
| Jogging | 8-12 | 5-7.5 | 2.2-3.3 | 4.3-6.5 |
| Cycling (recreational) | 15-25 | 9-16 | 4.2-6.9 | 8.1-13.5 |
| City driving | 30-50 | 19-31 | 8.3-13.9 | 16-27 |
| Highway driving | 100-130 | 62-81 | 27.8-36.1 | 54-70 |
| High-speed train | 250-320 | 155-200 | 69-89 | 135-173 |
| Commercial aircraft | 800-900 | 497-559 | 222-250 | 432-486 |
| Speed of sound (sea level) | 1235 | 767 | 343 | 667 |
Typical average speeds for common activities and vehicles. Actual speeds vary considerably.
Frequently asked questions
How do I calculate speed from distance and time?
Divide the total distance by the total time. Make sure both are in compatible units before dividing. For example, 150 km in 2 hours gives 75 km/h. If your time is in minutes or seconds, convert to hours first, or use the hours-minutes-seconds inputs in this calculator so the conversion is handled automatically.
How many km/h is 1 mph?
One mile per hour equals exactly 1.609344 kilometres per hour, because the international mile is defined as exactly 1,609.344 metres. To convert any mph figure to km/h, multiply by 1.609344. Going the other way, divide km/h by 1.609344 to get mph.
How do I convert km/h to m/s?
Divide by 3.6. One kilometre is 1,000 metres and one hour is 3,600 seconds, so 1 km/h = 1,000/3,600 m/s = 1/3.6 m/s. For example, 90 km/h = 25 m/s exactly. To go the other way, multiply m/s by 3.6 to get km/h.
What is a knot, and how does it compare to km/h?
A knot is one nautical mile per hour. One nautical mile is exactly 1,852 metres (it is defined as one minute of arc along a meridian of the Earth). So 1 knot = 1.852 km/h, and 1 km/h = about 0.5400 knots. Knots are the standard speed unit in aviation and maritime navigation because they relate directly to angular distance on the globe.
What is the difference between average speed and instantaneous speed?
Average speed is total distance divided by total elapsed time, regardless of how the speed varied during the journey. A vehicle speedometer shows instantaneous speed, the rate of motion at that precise moment. This calculator always computes average speed. If you stopped for 15 minutes during a 2-hour trip, those 15 minutes of zero speed pull the average down, even though your speedometer may have read 100 km/h while moving.
How do I solve for time instead of speed?
Use the "Solve for" selector at the top and choose "Time". Then enter the distance you need to cover and your expected average speed. The calculator divides distance by speed and displays the result in hours, minutes, and seconds. For example, a 300 km journey at 80 km/h takes 3 hours 45 minutes.