Braking Distance Calculator
Calculate total stopping distance based on speed, road conditions, and reaction time.
Supports both metric and imperial units.
How Braking Distance Is Calculated
Braking distance is the distance a vehicle travels from the moment the brakes are applied until it comes to a complete stop. It is separate from reaction distance (distance covered during the driver’s reaction time before braking begins).
Physics-based braking distance formula:
Braking Distance (m) = v² ÷ (2 × μ × g)
Where:
- v = initial speed in m/s
- μ = coefficient of friction between tires and road
- g = 9.81 m/s²
Speed conversion: mph × 0.447 = m/s
Typical friction coefficients:
| Condition | μ (dry) | μ (wet) |
|---|---|---|
| Concrete | 0.80 | 0.45 |
| Asphalt | 0.75 | 0.40 |
| Gravel | 0.60 | 0.40 |
| Snow | 0.20 | — |
| Ice | 0.10 | — |
Worked example — 60 mph on dry asphalt:
v = 60 × 0.447 = 26.8 m/s Braking distance = (26.8)² ÷ (2 × 0.75 × 9.81) = 718.24 ÷ 14.715 = 48.8 m (160 ft)
Add reaction distance at 1.5 seconds reaction time:
Reaction distance = 26.8 × 1.5 = 40.2 m (132 ft)
Total stopping distance = 48.8 + 40.2 = 89 m (292 ft)
Doubling speed quadruples braking distance — at 120 mph, braking distance alone exceeds 600 ft.
ABS (Anti-lock Braking System): Keeps μ at peak by preventing wheel lockup. Locked wheels actually slide at lower friction (kinetic μ < static μ), increasing stopping distance. ABS can reduce stopping distance by 10–30% on wet roads.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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