Speed Calculator
This speed calculator solves the distance–speed–time triangle for any unknown. Select whether you want to find speed, distance, or time, enter the two known values with your preferred units, and get the answer instantly.
Enter known values
Choose which variable to solve for, then enter the other two values.
The speed–distance–time triangle
The three quantities are linked by one formula. Covering the variable you want to find with your thumb reveals the calculation for the other two:
Speed = Distance ÷ Time
Distance = Speed × Time
Time = Distance ÷ Speed
The key rule is unit consistency: distance and speed units must correspond. If speed is in km/h, distance must be in km and time in hours. If speed is in m/s, distance must be in metres and time in seconds. The calculator handles this automatically through the unit dropdowns.
Speed conversion cheat-sheet
Common conversion factors (all approximate to 5 significant figures):
1 m/s = 3.6000 km/h = 2.2369 mph = 3.2808 ft/s
1 km/h = 0.27778 m/s = 0.62137 mph
1 mph = 1.60934 km/h = 0.44704 m/s
1 ft/s = 0.30480 m/s = 1.09728 km/h
Frequently asked questions
- What is the formula for speed?
- Speed equals distance divided by time: speed = distance ÷ time. This triangle relationship also lets you rearrange it: distance = speed × time, and time = distance ÷ speed. The calculator handles all three forms — just choose which variable you want to find.
- What is the difference between speed and velocity?
- Speed is a scalar quantity — it has magnitude only (e.g. 60 km/h). Velocity is a vector quantity — it has both magnitude and direction (e.g. 60 km/h north). For everyday distance–time problems like road trips or running, speed is the relevant quantity, which is what this calculator computes.
- How do I convert between km/h and mph?
- 1 mile per hour equals approximately 1.60934 kilometres per hour. To convert mph to km/h, multiply by 1.60934. To convert km/h to mph, divide by 1.60934 (or multiply by 0.62137). The calculator lets you enter distance in either kilometres or miles and time in hours, minutes, or seconds, so it handles the conversion automatically.
- How do I calculate average speed for a journey?
- Average speed equals total distance divided by total time — not the average of the individual speeds. For example, if you drive 100 km in 1 hour and then 100 km in 2 hours, your average speed is 200 km ÷ 3 hours ≈ 66.7 km/h, not (100 + 50) ÷ 2 = 75 km/h. Enter the total distance and total time into this calculator to get the correct average.
- What is acceleration and how is it related to speed?
- Acceleration is the rate of change of velocity over time: a = Δv ÷ Δt. When an object speeds up, slows down, or changes direction, it is accelerating. This calculator assumes constant speed — it does not model acceleration. For problems involving changing speed, you would also need Newton's Second Law and the kinematic equations.
- How fast is the speed of sound?
- The speed of sound in dry air at 20 °C is approximately 343 m/s, or about 1235 km/h (767 mph). This value varies with temperature and medium — sound travels faster in warmer air and much faster through liquids and solids. You can use this calculator to convert between units or compute distances at Mach speeds by entering 343 m/s as your speed.
- How do I find travel time given distance and speed?
- Select "Solve for Time" in the calculator, then enter your distance and speed. Time = distance ÷ speed. For example, a 300 km drive at 100 km/h takes 300 ÷ 100 = 3 hours. The calculator will express the result in the time unit you choose — hours, minutes, or seconds.