Braking Distance Calculator

Work out braking distance instantly with clear inputs, formula shown and shareable results.

About Braking Distance Calculator

Braking distance is v squared over 2 mu g, so it grows with the square of speed: doubling from 45 to 90 km/h quadruples it. Thinking distance grows only linearly, which is why speed matters so much more at higher velocities.

Formula

Stopping distance

d = v x t_reaction + v^2 / (2 x mu x g), with mu adjusted for gradient

Worked example

With the default values below, Braking Distance Calculator returns Total stopping distance of 71.86. Change any input above and every figure here is recalculated in your browser.

Inputs used

Speed: 90 km/h
Tyre-road friction coefficient: 0.7
Road gradient (downhill negative)accepts -30–30 %: -2 %
Reaction time: 1 s

Results

Total stopping distance: 71.86 m
Braking distance: 46.86 m
Thinking distance: 25.00 m
Deceleration: 6.67 m/s²

Step by step

1Values used
2Stopping distance
3Total stopping distance= 71.86 m
4Braking distance= 46.86 m
5Thinking distance= 25.00 m
6Deceleration= 6.67 m/s²

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What friction coefficients are realistic?

0.7-0.8 on dry asphalt, 0.4-0.6 wet, 0.2-0.3 on packed snow and as low as 0.1 on ice.

Why does speed matter so much?

Because kinetic energy scales with velocity squared, and all of it must be dissipated by the brakes. A 10% speed increase adds 21% to the braking distance.