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Stopping Distance Calculator

Reaction, braking and total stopping distance at any speed.

Best for: Understanding safe following distances and how speed and road conditions affect the distance needed to stop.

Complete guide
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How it's calculated & sources
The Stopping Distance Calculator uses the standard formula for this calculation. It runs entirely in your browser, so your inputs are never uploaded. Figures are educational estimates, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.

Free & no sign-up · runs entirely in your browser. Results are estimates for general information, not professional advice — verify important decisions with a qualified expert. Last reviewed June 2026.

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Complete guide

Quick answers

Short, sourced answers to the questions people (and AI assistants) ask most.

What is Stopping Distance?
A stopping distance calculator estimates how far a vehicle travels from the moment a hazard appears to a full stop — the reaction distance plus the braking distance.
Why does Stopping Distance matter?
Because the braking part scales with the square of speed, doubling your speed roughly quadruples the braking distance. Wet or icy roads lower the grip and lengthen it sharply — which is why speed and conditions matter so much for safety.
How is Stopping Distance calculated?
Reaction distance is your speed multiplied by your reaction time (around 1.5 seconds is a common assumption). Braking distance grows with the square of speed and depends on grip, so it is roughly speed squared divided by twice the friction times gravity. Total stopping distance is the two added together. Formula: Stopping distance = (speed x reaction time) + (speed^2 / (2 x friction x g)).
What are common stopping distance mistakes?
Assuming stopping distance rises in proportion to speed — the braking part is quadratic.
When should you use the Stopping Distance Calculator?
Understanding safe following distances and how speed and road conditions affect the distance needed to stop.

What is the Stopping Distance Calculator?

A stopping distance calculator estimates how far a vehicle travels from the moment a hazard appears to a full stop — the reaction distance plus the braking distance.

How the Stopping Distance Calculator works

Reaction distance is your speed multiplied by your reaction time (around 1.5 seconds is a common assumption). Braking distance grows with the square of speed and depends on grip, so it is roughly speed squared divided by twice the friction times gravity. Total stopping distance is the two added together.

Stopping distance = (speed x reaction time) + (speed^2 / (2 x friction x g))

Stopping distance by speed (dry road, 1.5 s reaction, μ ≈ 0.7)

30 km/h13 m5 m18 m
50 km/h21 m14 m35 m
70 km/h29 m28 m57 m
100 km/h42 m56 m98 m
120 km/h50 m81 m131 m

Key terms

Reaction distance:
Distance travelled while you perceive and react, before braking.
Braking distance:
Distance covered once the brakes are applied until stopped.

Common mistakes to avoid

  • Assuming stopping distance rises in proportion to speed — the braking part is quadratic.
  • Leaving out reaction time, which adds a large fixed distance.
  • Ignoring road surface, tire condition and weather, which change the grip dramatically.

Keywords: stopping, distance, braking, reaction.

Sources: US NHTSA — Speeding and safety

Reviewed by the Free Tools Galaxy editorial team · Updated June 2026 · Calculated privately in your browser.

Frequently asked questions

Is the Stopping Distance Calculator free to use?+

Yes. Every tool on Free Tools Galaxy is 100% free, runs in your browser and requires no signup.

How accurate is the Stopping Distance Calculator?+

Stopping Distance Calculator uses the standard stopping distance formula in double-precision arithmetic, so the same inputs always produce the same result and you can verify any figure by hand. It is an educational estimate — real-world outcomes depend on your actual rates, rules and assumptions.

Do you store my inputs?+

No. The Stopping Distance Calculator runs entirely in your browser. Nothing is uploaded or saved to a server.

Can I use the Stopping Distance Calculator on mobile?+

Yes — the interface is fully responsive and works on phones, tablets and desktops.

What are common mistakes to avoid?+

The most frequent mistake is mixing units. Double-check your inputs use a single, consistent unit before clicking Calculate.

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Reaction, braking and total stopping distance at any speed.

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