Stopping Distance Calculator
Calculate total stopping distance by speed, road condition, and reaction time.
Understand the difference between thinking distance and braking distance.
How Stopping Distance Is Calculated
Total stopping distance has two parts:
Total Stopping Distance = Thinking Distance + Braking Distance
Thinking distance is how far you travel while reacting before braking begins. Braking distance is how far you travel once the brakes are fully applied.
Thinking Distance Formula
Thinking Distance = Speed × Reaction Time
The average driver reaction time is 0.7–1.5 seconds. Distracted or tired drivers may react in 2–3 seconds or more.
Braking Distance Formula
Braking Distance = v² ÷ (2 × g × μ)
Where:
- v = speed in m/s
- g = 9.81 m/s² (gravity)
- μ (mu) = friction coefficient between tyres and road
Road Surface Friction Coefficients
| Road Condition | Friction Coefficient (μ) |
|---|---|
| Dry asphalt | 0.80 |
| Wet asphalt | 0.50 |
| Packed snow | 0.25 |
| Ice | 0.10 |
Typical Stopping Distances (Dry Road, 1s Reaction)
| Speed | Thinking | Braking | Total |
|---|---|---|---|
| 30 km/h (19 mph) | 8 m | 7 m | 15 m |
| 50 km/h (31 mph) | 14 m | 20 m | 34 m |
| 80 km/h (50 mph) | 22 m | 51 m | 73 m |
| 100 km/h (62 mph) | 28 m | 80 m | 108 m |
| 130 km/h (81 mph) | 36 m | 135 m | 171 m |
Key insight: Doubling your speed quadruples your braking distance. This is why speeding is so dangerous — the numbers grow exponentially.
Both metric (m/km) and imperial (ft/mph) results are shown.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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