Deceleration Calculator
Work out deceleration instantly with clear inputs, formula shown and shareable results.
About Deceleration Calculator
Deceleration over a known distance comes from v^2 = u^2 + 2as rearranged, which avoids needing the time. Braking from 100 km/h to 5 m/s in 60 m demands about 6.2 m/s2, or 0.63 g. Because kinetic energy goes as speed squared, most of the energy is removed in the first part of the stop.
Formulas
From speeds and distance
a = (v^2 - u^2) / (2s)
Time to slow
t = (v - u) / a
Worked example
With the default values below, Deceleration Calculator returns Deceleration of 6.223. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Initial speedminimum 0 m/s
- 27.78 m/s
- Final speedminimum 0 m/s
- 5 m/s
- Braking distanceminimum 0 m
- 60 m
Results
- Deceleration
- 6.223 m/s2
- Time To Slow Down
- 3.661 s
- Deceleration In g
- 0.635 g
- Share Of Kinetic Energy Removed
- 0.968%
Step by step
- 1Values used
- 2From speeds and distance
- 3Time to slow
- 4Deceleration= 6.223 m/s2
- 5Time To Slow Down= 3.661 s
- 6Deceleration In g= 0.635 g
- 7Share Of Kinetic Energy Removed= 0.968
Assumptions and limits
- The result is derived only from the 3 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 3 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
Why is doubling speed so much worse for braking?
Stopping distance goes with the square of speed, so twice the speed needs four times the distance at the same deceleration.
What deceleration can a car actually manage?
Around 0.8-1.0 g on dry asphalt with good tyres, roughly 8-10 m/s2. Wet roads cut that by a third or more.