Stopping Distance Calculator
An estimate of how far a car travels from the moment a driver sees a hazard until it stops. It adds the distance covered while reacting to the distance covered while braking. This is a physics estimate; real stops depend on tires, brakes, the road and conditions.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Reaction distance is your speed times the time it takes to notice the hazard and move to the brake. A common figure for reaction time is about 1.5 seconds.
Braking distance is speed squared divided by twice the road grip times gravity. Wet or icy roads have less grip, so the braking distance grows quickly.
Worked example
At 55 mph, with a reaction time of 1.5 s, the car covers 121 ft before the brakes start. Braking adds 144 ft, for a total stopping distance of 265 ft.
Questions
Why does stopping distance rise so fast with speed?
Braking distance goes with the square of speed, so doubling speed roughly quadruples it.
What grip number should I use?
Dry asphalt is often taken as around 0.7, and wet roads are lower. Ice is much lower. These are typical values, not measurements of your road.
Does this include the car's brakes or tires?
No. It assumes an ideal stop with the grip you enter. Worn tires, brake condition and load all change real results.
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