Speed Distance Time Calculator
The speed distance time calculator solves the standard SDT relationship from any two known values. Use it to find speed from distance and time, find distance from speed and time, or find time from distance and speed. The calculator supports common road, aviation, physics, and everyday units, including m/s, km/h, mph, knots, metres, kilometres, miles, feet, seconds, minutes, and hours.
How to Use
- Select Find Speed, Find Distance, or Find Time according to the unknown value.
- Enter the two known values in the labelled fields for the active mode.
- Choose the correct unit beside each input before calculating.
- Select the result unit you want, such as km/h for road speed or m/s for physics work.
- Click Calculate and read the main result plus the step note showing which formula was used.
SDT Formula
Distance = Speed x Time
Time = Distance / Speed
The speed, distance, and time relationship is one of the most common formulas in motion problems. Speed measures how fast distance is covered. Distance measures how far an object travels. Time measures how long the motion lasts. If distance is in metres and time is in seconds, speed is in metres per second. If distance is in kilometres and time is in hours, speed is in kilometres per hour. The formula is simple, but unit consistency is essential.
This calculator converts all distances to metres, times to seconds, and speeds to metres per second internally. After solving the formula, it converts the answer back to the result unit you selected. That conversion step prevents common mistakes such as dividing kilometres by minutes and accidentally calling the result km/h. It also allows mixed inputs, such as miles and minutes, while keeping the calculation mathematically clean.
Worked Example
A car travels 300 km in 3.5 hours. Speed = distance / time = 300 / 3.5 = 85.71 km/h. To express the same speed in m/s, divide km/h by 3.6: 85.71 / 3.6 = 23.81 m/s. To express it in mph, divide kilometres per hour by 1.609344: 85.71 / 1.609344 = 53.26 mph.
If the driver keeps the same average speed for 5 hours, distance = speed x time = 85.71 x 5 = 428.55 km. If the distance is fixed at 300 km and the speed falls to 60 km/h because of traffic, time = distance / speed = 300 / 60 = 5 hours.
Speed of Common Things
| Object | Speed (km/h) | Speed (m/s) | Speed (mph) |
|---|---|---|---|
| Snail | 0.05 | 0.01 | 0.03 |
| Walking human | 5 | 1.4 | 3.1 |
| Cyclist | 20 | 5.6 | 12.4 |
| Car (city) | 50 | 13.9 | 31.1 |
| Car (highway) | 100 | 27.8 | 62.1 |
| Cheetah | 120 | 33.3 | 74.6 |
| Train (express) | 200 | 55.6 | 124.3 |
| Commercial aircraft | 900 | 250 | 559 |
| Speed of sound | 1235 | 343 | 767 |
| Speed of light | 1,079,251,200 | 299,792,458 | 670,616,629 |
Average Speed in Real Travel
The calculator gives average speed, not moment-by-moment speed. A car that travels 300 km in 3.5 hours may have moved at 110 km/h on open highway, slowed to 20 km/h in traffic, and stopped for tolls or signals. The average speed includes every part of the trip if the total time includes those stops. For trip planning, this is usually what matters because arrival time depends on total distance divided by total elapsed time. For vehicle performance or physics experiments, you may need instantaneous speed from a speedometer, sensor, or data logger.
Speed and time estimates are also sensitive to assumptions. A route shown as 100 km can take one hour on a motorway or three hours on hilly roads. Cyclists and runners often track pace, which is the inverse of speed: time per kilometre or time per mile. You can still use the SDT formula by converting pace into speed or by calculating time directly from distance and known pace. In safety contexts, remember that stopping distance increases rapidly with speed because braking energy depends on speed squared, not just speed itself.
FAQ
What is the formula for speed?
The formula for speed is speed = distance divided by time. If a vehicle travels 120 kilometres in 2 hours, its average speed is 120 / 2 = 60 km/h. The same formula works in any unit system if the units match. Metres divided by seconds gives m/s, kilometres divided by hours gives km/h, and miles divided by hours gives mph. When units are mixed, convert them first or use a calculator that converts internally.
What is the difference between speed and velocity?
Speed is a scalar quantity, meaning it has magnitude only. Velocity is a vector quantity, meaning it has both magnitude and direction. A car moving at 60 km/h has a speed of 60 km/h. If it is moving 60 km/h north, that is a velocity. In everyday travel, speed is often enough. In physics, direction matters because turning around, moving in circles, or changing direction can change velocity even when the speedometer reading stays the same.
What is average speed?
Average speed is total distance divided by total elapsed time. It smooths out faster and slower parts of a journey into one value. If you drive 50 km in the first hour and 100 km in the second hour, your average speed over the two hours is 150 / 2 = 75 km/h. Average speed is useful for trip planning, race summaries, and comparing journeys. It does not tell you the highest speed reached or how speed changed during the trip.
How do I convert km/h to m/s?
To convert kilometres per hour to metres per second, divide by 3.6. This works because one kilometre is 1000 metres and one hour is 3600 seconds, so 1 km/h = 1000 / 3600 m/s = 0.27778 m/s. For example, 90 km/h divided by 3.6 equals 25 m/s. To convert m/s back to km/h, multiply by 3.6. This conversion is common in physics, road safety, sports timing, and engineering calculations.
What is acceleration?
Acceleration is the rate at which velocity changes with time. If speed increases, decreases, or changes direction, acceleration is present. The common unit is m/s^2, meaning metres per second per second. A car that goes from 0 to 100 km/h in 10 seconds has positive acceleration. Braking produces negative acceleration, often called deceleration. Acceleration is related to speed but is not the same formula as speed distance time. The SDT calculator assumes average speed over a time interval, not changing speed under acceleration.