Speed calculator
Speed = distance ÷ time. Fill any two fields — the third is calculated, along with the value in m/s and mph.
The last edited field decides what is solved: distance + time → speed, distance + speed → time, time + speed → distance.
The formulas
| Solve for | Formula | Example |
|---|---|---|
| Speed | v = s ÷ t | 150 km ÷ 1.5 h = 100 km/h |
| Time | t = s ÷ v | 300 km ÷ 120 km/h = 2.5 h |
| Distance | s = v × t | 80 km/h × 0.75 h = 60 km |
Unit trap: convert minutes to hours (÷ 60) before dividing — 90 minutes is 1.5 h, not 90. The calculator handles that for you.
Speed in practice: runners, cyclists, drivers
| Activity | pace | km/h |
|---|---|---|
| Walking | 12–15 min/km | 4–5 |
| Jogging | 6–7 min/km | 8.5–10 |
| 10K in 50 minutes | 5 min/km | 12 |
| Casual cycling | – | 15–20 |
| Road bike | – | 25–35 |
| Car, motorway average | – | 90–110 |
Related: mph ↔ km/h for imperial speeds, knots ↔ km/h for wind and boats, and the driving time calculator for trip planning.
Braking distance: the other side of speed
Driving-school rules of thumb (metric): reaction distance ≈ (speed ÷ 10) × 3 metres for one second of reaction; braking distance ≈ (speed ÷ 10)² metres. At 100 km/h that is 30 m of reaction plus 100 m of braking — 130 m to a full stop. Braking distance grows with the square of speed: double the speed, four times the distance.
Speed-camera "average speed check" zones use exactly this page's formula in reverse: they time you between two gantries and compute v = s ÷ t.
Frequently asked questions
How do you calculate speed in km/h?
Speed = distance ÷ time. 150 km in 1.5 hours is 100 km/h. This calculator solves the formula for any of the three values — enter two, get the third.
How do you convert km/h to m/s?
Divide by 3.6: 100 km/h = 27.8 m/s. The other way, multiply by 3.6: 10 m/s = 36 km/h.
What is pace and how does it relate to speed?
Runners use minutes per kilometre: pace = 60 ÷ km/h. 10 km/h equals a 6:00 min/km pace; a 5:00 min/km pace is 12 km/h.
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