Stopping Distance Calculator
This stopping distance calculator works out how far a vehicle travels from the moment the driver sees a hazard to a full stop. Enter the speed, the reaction time, the road surface, and the grade, and the stopping distance calculator splits the total into reaction distance and braking distance, in feet and meters, along with the time to stop.
Results
The Stopping Distance Calculator is part of our Performance collection. Browse more performance to size, convert, and check your work alongside this tool.
What the stopping distance calculator does
Stopping happens in two parts. During the reaction time the car keeps going at full speed while the driver sees the hazard and moves to the brake. Then the brakes slow the car at a rate set by the grip between tire and road. The stopping distance calculator adds the two, using the friction coefficient of the surface and the slope of the road.
Stopping distance formula
v is the speed in m/s, t the reaction time, g = 9.81 m/s², μ the tire-road friction coefficient, and G the grade as a decimal. Braking distance grows with the square of speed, so doubling the speed roughly quadruples it, while reaction distance only doubles.
Stopping distance at 60 mph example
60 mph is 26.82 m/s. With a 1.5 s reaction on a dry road (μ = 0.7):
Total stopping distance is 304 ft (92.6 m), about 5.4 seconds from seeing the hazard to standstill.
How to use the braking distance calculator
Enter the speed and choose mph or km/h. Keep 1.5 seconds for reaction time, a common design value; an alert driver may react in under a second, a distracted one in two or more. Choose the road surface and enter the grade as a percentage, positive uphill and negative downhill. Press Calculate.
Reading your total stopping distance
The total is for a car with good brakes and tires on a level road. Worn tires, heavy loads, and downhill grades add distance. On a wet road the braking part grows by about 75% compared with dry, and on ice it can be seven times longer. Keep a following gap of at least three seconds so the reaction part never catches you out.
When to use a car stopping distance calculator
- Learning stopping distances for a driving test
- Setting a safe following distance
- Comparing dry and wet road braking
- Accident reconstruction estimates
- Road and parking lot design checks
Common stopping distance calculator mistakes
- Forgetting reaction time. It is often the larger part at low speeds.
- Using dry friction in rain. Choose the real surface.
- Ignoring downhill grades. A negative grade adds distance.
- Mixing mph and m/s. The calculator converts for you.
Tips for stopping distance wet road driving
- Double your following gap in rain.
- Check tire tread depth regularly.
- Slow down before curves and downhill stretches.
Braking distance formula and kinetic energy
The brakes must turn all of the car's kinetic energy, ½ m v², into heat through friction. Friction force is μ m g, so the distance needed is ½ m v² ÷ (μ m g) = v² ÷ (2 μ g). Mass cancels, which is why a light car and a heavy one with equal tires stop in similar distances. The kinetic energy calculator shows how fast that energy grows with speed, and the friction force calculator gives the braking force.
Reaction distance and following gaps
At 60 mph a car covers 88 ft every second, so a 1.5 s reaction uses 132 ft before braking starts. A three-second gap gives 264 ft, enough to cover the reaction and part of the braking when the car ahead also brakes. The speed distance time calculator converts any gap in seconds to feet or meters at your speed.
Stopping distance chart (1.5 s reaction)
| Speed | Dry (0.7) | Wet (0.4) | Snow (0.2) |
|---|---|---|---|
| 20 mph | 63 ft | 77 ft | 111 ft |
| 30 mph | 109 ft | 141 ft | 216 ft |
| 40 mph | 164 ft | 222 ft | 355 ft |
| 50 mph | 229 ft | 319 ft | 528 ft |
| 60 mph | 304 ft | 433 ft | 734 ft |
| 70 mph | 388 ft | 564 ft | 973 ft |
| 80 mph | 482 ft | 711 ft | 1246 ft |
Stopping Distance Calculator FAQ
What is the stopping distance at 60 mph?
About 304 ft on a dry road with a 1.5 s reaction: 132 ft of reaction distance and 172 ft of braking.
How do you calculate stopping distance?
Add the reaction distance, speed × reaction time, to the braking distance, speed² ÷ (2 × g × friction).
How much longer is stopping distance on a wet road?
The braking part grows by about 75% at a friction of 0.4 instead of 0.7. At 60 mph the total rises from 304 ft to about 433 ft.
What is thinking distance?
Another name for reaction distance, the ground covered before the brakes are applied.