Estimate reaction, braking and total stopping distance at any speed.
Calculated locally in your browser.
How is stopping distance calculated?
Reaction distance = speed × reaction time, and braking distance = v² ÷ (2 · μ · g), where v is speed in m/s, μ is grip and g ≈ 9.81 m/s²; total stopping distance is their sum. Because braking depends on speed squared, doubling speed roughly quadruples it. At 100 km/h with a 1.5 s reaction and dry grip, total is about 97.8 m.
Understanding your result
Because braking distance depends on the square of speed, small increases in speed add a lot of distance — doubling speed roughly quadruples the braking part. Wet, snowy or icy roads lower the grip coefficient, dramatically increasing the distance needed. Real figures also depend on tyres, brakes, load and gradient.
Formula and method
Reaction distance = speed × reaction time. Braking distance = v² ÷ (2 · μ · g), where v is speed in m/s, μ is the grip coefficient and g ≈ 9.81 m/s². Total stopping distance is the sum.
Worked example
At 100 km/h (27.8 m/s) with a 1.5 s reaction and dry grip (μ 0.7): reaction ≈ 41.7 m, braking ≈ 56.2 m, total ≈ 97.8 m.
How to use this tool
- Enter your speed and choose the unit.
- Set your reaction time (around 1.5 s is typical).
- Pick the road condition.
- Read the reaction, braking and total distances.
Common mistakes to avoid
- Assuming braking distance scales with speed — it scales with speed squared.
- Using dry-road grip in wet or icy conditions.
- Forgetting reaction time, which adds distance before braking even starts.
About the Stopping Distance Calculator
The Stopping Distance Calculator estimates how far a vehicle travels before it halts — the reaction distance while you respond plus the braking distance while the car slows. It works in metres and feet for any speed and road condition.
Who should use this tool
Learner and experienced drivers, instructors, fleet managers and road-safety educators.
Benefits
- Reaction, braking and total distance in one go.
- Results in both metres and feet.
- Presets for dry, wet, snow and icy roads.
- Private — calculated entirely in your browser.
Practical use cases
- Understanding safe following distances.
- Teaching how speed affects braking.
- Comparing stopping distances on wet versus dry roads.
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Frequently asked questions
What is a typical reaction time?
Around 1 to 1.5 seconds for an alert driver. Tiredness, distraction or alcohol make it longer.
Why does wet road increase stopping distance so much?
Water lowers the grip coefficient, so the same speed needs far more distance to brake — often roughly double that of a dry road.
Does this include the car's own performance?
It uses a grip coefficient as a general model. Actual stopping distance also depends on tyres, brakes, vehicle weight and the road surface.