Stopping Distance Calculator

Calculate thinking distance, braking distance and total stopping distance at any speed — essential for theory test prep and safer driving.

Speed (mph)

Road conditions

Driver reaction

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Fill in the details to get your result.

How This Works

Thinking (reaction) distance = speed × reaction time. Highway Code uses 2/3 second reaction time. Braking distance uses the formula: v² ÷ (2 × g × friction coefficient), adjusted for road conditions. A dry road has a friction coefficient of ~0.7. Wet roads reduce this to ~0.35 (doubles stopping distance). Ice reduces it to ~0.1 (10× dry distance).

Key figures: 20mph = 12m (40ft). 30mph = 23m (75ft). 40mph = 36m (118ft). 50mph = 53m (175ft). 60mph = 73m (240ft). 70mph = 96m (315ft). These are based on a normal dry road with 2/3 second reaction time. Remember: these double in wet conditions and multiply by 10 on ice. The 2-second rule (maintain a 2-second gap) approximates safe following distance at most speeds.