Find speed from distance and time.
The most basic motion formula — distance divided by the time taken to cover it.
Speed: Distance ÷ Time
This calculator finds average speed from the distance covered and the time taken. You enter the distance in kilometres and the time in hours, and it returns the speed in km/h. Rearranged, the same relationship answers how far you can go or how long a journey will take.
Speed, distance and time is one of the first formulas students meet in physics and in aptitude tests, and one of the most used in daily life. Drivers use it to judge whether they will reach a train station in time, cyclists and runners to track their average, logistics planners to estimate delivery windows, and students to solve the classic train and boat problems that appear in board exams and competitive exams.
1. Measure the total distance in kilometres.
2. Measure the total time in hours. Convert minutes by dividing by 60, so 2 hours 30 minutes is 2.5 hours.
3. Speed = Distance ÷ Time, in km/h.
4. If you need distance, rearrange: Distance = Speed × Time.
5. If you need time, rearrange: Time = Distance ÷ Speed.
6. To convert km/h to metres per second, divide by 3.6.
Speed is the distance covered per unit of time. If a car covers 120 km in 2 hours, it covers 60 km in each hour on average. The formula s = d ÷ t is just the definition of that rate. It gives the average speed over the whole journey, not the speed at any particular moment, which is what the speedometer shows. In physics, velocity also includes direction, but for road journeys speed is what matters.
If you drive 60 km at 30 km/h and return at 60 km/h, the average is not 45 km/h. The first leg takes 2 hours and the second 1 hour, so you cover 120 km in 3 hours, an average of 40 km/h. For two equal distances at speeds a and b, the average speed is 2ab ÷ (a + b), the harmonic mean. Always divide total distance by total time, including stops if you want door-to-door speed.
Time in hours and minutes is not a decimal. Two hours thirty minutes is 2.5 hours, not 2.30. Forty-five minutes is 0.75 hours. For metres per second, remember that 1 km/h is 1000 metres in 3600 seconds, so divide km/h by 3.6 to get m/s, and multiply m/s by 3.6 to get km/h. A speed of 72 km/h is 20 m/s, a pair of numbers that appears in many textbook problems.
Suresh drove 385 km on the highway to his hometown, and the whole drive, including one tea break, took 6.5 hours.
Answer: Speed 59.23 km/h
Typing 1 hour 30 minutes as 1.30 instead of 1.5.
Averaging the speeds of different legs instead of dividing total distance by total time.
Mixing units, for example distance in metres with time in hours.
Treating average speed as the highest speed reached, or as the speed you must hold the whole way.
Forgetting that stops count towards journey time if you want door-to-door average speed.
Estimating travel time for road trips and commutes.
Solving speed, distance and time questions in school and competitive exams.
Checking average speeds for cycling, running or driving logs.
Planning delivery schedules and pickup windows.
What if I know speed and distance but need time?
Use the same formula the other way round: Time = Distance ÷ Speed. This calculator is set up to find speed, when you already know the other two.