Reaction Distance Calculator

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

About Reaction Distance Calculator

Reaction distance is speed times reaction time, entirely linear. At 100 km/h the car travels 27.8 m every second, so an extra half second of distraction adds nearly 14 m — more than three car lengths before the brakes are even applied.

Formula

Reaction distance

d = v x total reaction time, with v in m/s

Worked example

With the default values below, Reaction Distance Calculator returns Reaction distance of 47.22. Change any input above and every figure here is recalculated in your browser.

Inputs used

Speed: 100 km/h
Reaction time: 1.2 s
Additional distraction delay: 0.5 s
Impairment multiplier: 1 x

Results

Reaction distance: 47.22 m
Distance at the base reaction time: 33.33 m
Extra distance from delay and impairment: 13.89 m
Total reaction time: 1.70 s

Step by step

1Values used
2Reaction distance
3Reaction distance= 47.22 m
4Distance at the base reaction time= 33.33 m
5Extra distance from delay and impairment= 13.89 m
6Total reaction time= 1.70 s

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 is a normal reaction time?

0.7-1.0 seconds for an alert driver expecting a hazard, 1.5 seconds or more when surprised. Highway design typically assumes 2.5 seconds.

How much does a phone add?

Texting adds one to three seconds of eyes-off-road time, which at motorway speed is 30-80 m travelled effectively blind.