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Speed, distance and time are locked together by one relationship: know any two and the third follows. Pick what to solve for, enter the other two values, and the calculator solves the matching equation. The only real trap is mixing units, keep distance and speed in matching pairs (km with km/h, miles with mph).
Speed, distance and time are locked together by a single relationship. Knowing any two values determines the third:
- Speed = distance ÷ time: 120 km in 2 hours = 60 km/h. - Distance = speed × time: 60 km/h for 2.5 hours = 150 km. - Time = distance ÷ speed: 300 km at 75 km/h = 4 hours.
This is the v = d/t triangle from physics, cover the value you want to find and the other two show you the operation. Every speed question, from journey planning to race timing, is one of these three.
Choose what to solve for, speed, distance or time, then enter the two values you know and press Calculate. If you are solving for speed, enter distance and time; the speed field is only needed when solving for distance or time.
Keep your units consistent: kilometres with km/h, miles with mph. The calculator works in km/h and km by default; convert other units first (1 mile = 1.609344 km) for an exact answer.
Different fields default to different speed units: roads use mph or km/h, physics uses m/s, aviation and marine navigation use knots. The fixed conversion factors:
- 1 mph = 1.609344 km/h (exact), so 100 km/h = 62.137 mph - 1 m/s = 3.6 km/h, so 10 m/s = 36 km/h, and 90 km/h = 25 m/s - 1 knot = 1.852 km/h ≈ 1.151 mph, one nautical mile per hour - 1 ft/s = 0.3048 m/s
A marathon in exactly 4 hours is 42.195 ÷ 4 = 10.549 km/h, which is 6.555 mph or 2.93 m/s, the same speed in three different units.
This catches people constantly. Drive 60 km at 60 km/h, then 60 km at 30 km/h. The average of 60 and 30 is 45, but your average speed is not 45 km/h: the first leg takes 1 hour and the second takes 2 hours, so you covered 120 km in 3 hours, an average of 40 km/h.
Average speed is always total distance divided by total time. When equal distances are covered at different speeds, the correct average is the harmonic mean, which is always lower than the arithmetic average, because you spend longer at the slower speed.
Runners think in pace, minutes per kilometre or per mile, which is the inverse of speed: pace = 60 ÷ speed in km/h. At 12 km/h your pace is 5:00 per km; at 10 km/h it is 6:00 per km.
The inverse relationship is why small speed changes feel big: going from 10 to 11 km/h sounds like 10%, but pace moves from 6:00/km to 5:27/km, more than 20 minutes over a marathon. Pace also maps directly onto what a running watch shows mid-run.
The arithmetic of speed is trivial; the errors come from units. Entering time in minutes with a speed in km/h throws the answer off by a factor of 60, a 25-minute 5K is 5 km ÷ 0.4167 h = 12 km/h, not 5 ÷ 25. Mixing metres with an hourly speed is off by 3,600.
The rule: convert time to hours (or everything to seconds) before dividing. 1 h 36 min = 1.6 h; 1 h 30 min = 1.5 h. Keep distance and speed in the same system, km with km/h, miles with mph, and the formula cannot go wrong.
Speed = distance ÷ time. Example: driving 240 km in 3 hours is 240 ÷ 3 = 80 km/h. Distance = speed × time, and time = distance ÷ speed are the same relationship rearranged.
Distance = speed × time. At 60 km/h for 2.5 hours you cover 60 × 2.5 = 150 km. At 900 km/h for 2.5 hours a plane covers 2,250 km.
Time = distance ÷ speed. Covering 300 km at 75 km/h takes 300 ÷ 75 = 4 hours. A marathon (42.195 km) at 10 km/h takes about 4.22 hours.
Average speed over the whole journey, total distance divided by total time. It does not account for stops, traffic or speed changes along the way.
Multiply by 0.621371. So 100 km/h = 62.137 mph, and going the other way, mph × 1.609344 = km/h (60 mph ≈ 96.56 km/h). The quick mental version is mph × 1.6.
Divide by 3.6. 36 km/h = 10 m/s; 90 km/h = 25 m/s. Going the other way, multiply m/s by 3.6. Physics problems and sports science almost always use m/s, while roads use km/h or mph.
One knot is one nautical mile per hour, and a nautical mile is exactly 1,852 metres, one arcminute of latitude. A knot is about 1.852 km/h or 1.151 mph, and it is the standard speed unit at sea and in aviation.
Speed is distance per time (km/h); pace is time per distance (minutes per km), they are inverses. Pace = 60 ÷ speed in km/h, so 12 km/h is 5:00 per km. Runners prefer pace because watches show it directly.
Because you spend more time at the slower speed, it carries more weight. Drive 60 km at 60 km/h then 60 km at 30 km/h: that is 1 hour + 2 hours for 120 km = 40 km/h, not the 45 km/h you get by averaging 60 and 30. Average speed is always total distance ÷ total time.