Braking Distance Calculator
Calculate braking distance and total stopping distance (including reaction time) at a given speed and friction.
How to use the calculator
- Enter the car's speed.
- Choose the road surface (dry/wet asphalt, snow, or ice) to set a typical friction coefficient, or adjust the reaction time.
- See reaction distance, braking distance, and total stopping distance.
How is it calculated?
The reaction distance is how far the car travels while the driver reacts, before braking actually starts — speed × reaction time. The braking distance uses the formula d = v² / (2·μ·g), where v is speed in m/s, μ is the friction coefficient, and g is gravitational acceleration. Total stopping distance is the sum of both.
Frequently asked questions
Why is the reaction distance so long?
Because the car keeps moving at full speed while the driver perceives the hazard and moves their foot to the brake — at 80 km/h (22.2 m/s) and 1 second of reaction time, the car travels over 22 meters before braking even starts.
Why does braking distance quadruple when speed doubles?
Because braking distance is proportional to the square of speed (v²) — double the speed, and you quadruple the braking distance, given the same friction.
Is 1 second a realistic reaction time?
1 second is a commonly used average estimate for a rested, attentive driver. Fatigue, distraction (like phone use), or alcohol can significantly increase reaction time — feel free to adjust the number to see the effect.