Find a car’s stopping distance — reaction plus braking — from the speed, the reaction time and the road condition (dry, wet, snow).
Speed and conditions
Enter the speed and the reaction time (typically ~1 s), then pick the road condition.
Physics estimate (tyres and brakes in good condition). Braking distance grows with the square of speed: double the speed → 4× the distance (e.g. 100→300 km/h is 9×). At very high speeds, aerodynamic drag and downforce shorten the real distance a little versus this idealised model. In reality the car, tyres and road also matter.
Stopping distance = 27.9 mQuick calculations for drivers. Standard formulas for consumption, cost and speed. Instant in-browser calculation, no account, no data sent. Fuel prices are indicative.
Stopping distance adds the reaction distance (speed × time) to the braking distance (grows with the square of speed):
At 50 km/h, with 1 s reaction on dry road: ≈ 13.9 m reaction + 14 m braking ≈ 28 m total.
It is the total distance travelled from the moment you spot a hazard until a complete stop. It is the sum of the reaction distance and the braking distance.
Braking distance grows with the square of speed: v² ÷ (2 × μ × g), where μ is the road grip and g is gravity. That is why doubling the speed makes braking four times longer.
It is the distance travelled while you react (typically ~1 second), before pressing the brake. It is speed × reaction time.
On dry road, with 1 second reaction, it is about 14 m reaction + 14 m braking, so roughly 28 m in total. On wet or snow, the distance increases significantly.
Because braking distance depends on the square of speed. At 100 km/h versus 50 km/h, the energy to dissipate is four times greater, and so is the braking distance.
They lower the grip (μ coefficient): from ~0.7 on dry to ~0.4 on wet and ~0.2 on snow. The lower the grip, the longer the braking distance.
It is a safety rule: keep at least 2 seconds behind the car in front (more on wet roads). This gives you reaction time and braking space.