🛑 Stopping Distance Calculator
Enter your speed, reaction time and the tyre–road grip to get the reaction, braking and total stopping distances.
Total stopping distance
84 m
Reaction distance
27.8 m
Braking distance
56.2 m
Total stopping distance is reaction distance (speed × reaction time) plus braking distance (v² ÷ 2μg), where μ is the tyre–road friction coefficient. Braking distance grows with the square of speed — doubling your speed quadruples it — and grip falls sharply in the wet, snow and ice. Real distances also depend on the vehicle, tyres and brakes; this is a physics estimate. 🔒 In your browser.
How the stopping distance calculator works
Stopping distance has two parts: the reaction distance you travel before braking (speed × reaction time) and the braking distance once the brakes are applied (v² ÷ 2μg, where μ is the tyre–road friction coefficient and g gravity). The tool adds them for the total, in metres or feet, with grip presets for dry, wet, snow and icy roads.
Braking distance grows with the square of speed, so doubling your speed roughly quadruples the braking distance — the single most important thing to understand about speed and safety. Grip (μ) falls dramatically off dry tarmac: roughly 0.7 dry, 0.4 wet, 0.2 snow, 0.1 ice. This is an idealised physics estimate; real distances depend on the vehicle, tyres, brakes and surface.
Frequently asked questions
How do you calculate stopping distance?
Add the reaction distance (speed × reaction time) to the braking distance (v² ÷ 2μg). At 100 km/h with a 1-second reaction on dry road (μ ≈ 0.7), that's about 28 m reacting plus 56 m braking — roughly 84 m total.
Why does stopping distance increase so much with speed?
Because braking distance depends on the square of speed (v²). Doubling your speed quadruples the braking distance, so a small increase in speed adds a lot of stopping distance — and energy to dissipate.
How does the road surface affect stopping distance?
Through the friction coefficient μ. Grip drops from about 0.7 on dry tarmac to 0.4 wet, 0.2 on snow and 0.1 on ice — so braking distance can be several times longer in poor conditions at the same speed.
What is a typical reaction time?
About 1 to 1.5 seconds for an alert driver; longer if distracted, tired or impaired. Reaction distance is speed × reaction time, so at highway speeds even a second means many metres travelled before braking begins.
Does this account for my specific car?
No — it's a physics estimate based on grip, not your vehicle's exact brakes, tyres, weight or ABS. Modern cars can approach these figures on good tyres; worn tyres or brakes do worse. Treat it as a guide, not a guarantee.