Braking & Reaction Distance Calculator
See how far your car travels before you even hit the brake, and how far it takes to stop — by speed, reaction time and road surface.
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Two Distances, Not One
The total distance a car covers before stopping has two separate parts: the reaction distance — how far it travels while you're still reacting, before your foot even touches the brake (speed × reaction time) — and the braking distance — how far it travels while actually slowing down, which depends on speed squared and the road's friction (dry asphalt grips far better than wet, snow or ice).
Both add up fast: doubling your speed doesn't just double the braking distance, it quadruples it, because braking distance scales with the square of speed.
Frequently Asked Questions
Why does doubling speed more than double the stopping distance?
Reaction distance scales linearly with speed (2× speed = 2× reaction distance), but braking distance scales with speed squared (2× speed = 4× braking distance) — physics of kinetic energy. That's why high-speed stops take disproportionately more room.
What reaction time should I use?
A typical alert driver reacts in about 1-1.5 seconds; distraction, fatigue or intoxication can push it well past 2-2.5 seconds. The default here (1.5s) is a commonly cited average — adjust it to see the effect.
How accurate are the road-surface friction values?
They're representative approximations (dry asphalt, wet asphalt, snow, ice), not measurements of your specific tires, tread depth or vehicle. Real stopping distance also depends on brake condition and ABS — treat this as an educational estimate, not a safety guarantee.
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Braking & Reaction Distance Calculator