How to use this calculator
- Enter speed. Set the initial road speed.
- Enter reaction time. Use driver, sensor or system delay before braking starts.
- Enter deceleration. Set average braking deceleration in g.
- Read distance. Review reaction distance, braking distance and total stopping distance.
How it works
Reaction distance is speed x reaction time. Braking distance is speed^2 / (2 x deceleration), where deceleration is the entered g value multiplied by standard gravity.
Use the brake heat calculator to turn the same speed change into stop energy, or the brake bias calculator for front/rear brake balance.
Worked example
Verified against the live calculator
From 60 mph with 1.5 s reaction time and 0.8 g braking, total stopping distance is about 87 m, with roughly 40 m from reaction delay.
Frequently asked questions
What does total stopping distance include?
It includes reaction distance plus braking distance from the entered speed and deceleration.
What deceleration should I use?
Use measured data when possible. A normal hard stop on good tires may be around 0.7-1.0 g, but surface and tire condition matter.
Does this include grade?
No. This version assumes a level road and constant average braking deceleration.
Why is reaction time separate?
At highway speed, reaction distance can be a large part of the total distance even before braking begins.
Method & assumptions
- Assumes constant average deceleration on level ground.
- Surface, tires, ABS, grade, brake fade, load and weather can change the real result substantially.