Created By : Naaz Fatima

Reviewed By : Phani Ponnapalli

Last Updated : Apr 10, 2023

Stopping Distance Calculator is a free tool that displays the stopping distance of a car. This tool makes it easy for you to calculate the stopping distance by taking the car speed, perception-reaction time, grade, road conditions and tap the calculate button.

Perception - reaction time:
The road is..

Detailed Steps to Find the Stopping Distance

The following are the steps to get the stopping distance of a vehicle easily. Go through these guidelines and obtain the result in a blink of an eye.

  • Make a note of the coefficient of friction, car speed, perception-reaction time.
  • Multiply the speed of the car with 0.278 and perception-reaction time
  • Add coefficient of friction, grade of the road and multiply it with 254
  • Divide the square of car speed by the product.
  • Add the results from step 2 and step 4 to get the stopping distance.

Stopping and Braking Distance | Perception-reaction Time

If you are driving your car on a street road. Suddenly, you notice an old person crossing the road ahead of you. The time from you see the event, before reacting to it is called the perception time. You might think that you hit the brake immediately, but there is a small delay between the moment you notice the danger and start to decelerate. This delay is also called the reaction time.

After hitting the brake, the car will move slowly towards the old person until it comes to stop. The distance travelled from the moment you press the brake is the braking distance. The total distance travelled during the perception-reaction time added with the braking distance is the stopping distance.

AASHTO Formula

Calculate stopping distance of car travels using the AASHTO (the American Association of State Highway and Transportation Officials). This AASHTO formula is used in road design for establishing the minimum stopping sight distance. The stopping distance depends on the road conditions such as dry or wet, speed of the car, perception-reaction time and others. AASHTO Formula is along the lines:

s = (0.278 x t x v) + v┬▓/(254 x (f + G))


f is the coefficient of friction between the tires and the road. It is equal to 0.7 for a dry road and ranges from 0.3 to 0.4 on a wet road.

s is the stopping distance

t is the perception-reaction time

v is the speed of the car

G is the grade (slope) of the road. It is positive for an uphill grade and negative for a road-going downhill.


Question: A car is moving with a velocity of 50 m/s on a dry road and suddenly applies brakes. If the perception-reaction time is 10 seconds, grade is 0.2% and find the stopping distance.


Given that,

velocity of car v = 50 m/s

perception-reaction time t = 10 seconds

Grade G = 0.2%

coefficient of friction f = 0.7

Stopping distance s = (0.278 x t x v) + v┬▓/(254 x (f + G))

s = (0.278 x 10 x 50) + 50┬▓/(254 x (0.7 + 0.2))

s = 139 + 2500/228.6

= 149.93

Therefore, the car stopping distance is 149.93 m.

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Frequently Asked Questions on Stopping Distance Calculator

1. How to calculate the stopping distance?

The stopping distance of a car can be calculated using the AASHTO formula. Get the perception-reaction time, grade, and speed details. Substitute the values in the formula and solve to get the car stopping distance.

2. What is the stopping distance at 30 mph?

Speed = 30 miles per hour = 13.41 meters per second

Stopping distance s = (0.278 x t x v) + v┬▓/(254 * (f + G))

s = (0.278 x 0 x 13.41) + 13.41┬▓/(254 * (0.3 + 0))

= 179.82/76.2 = 2.3

The stopping distance at 30 miles per hour is 23 meters

3. What is the AASHTO formula?

The AASHTO formula to find the stopping distance is s = (0.278 x t x v) + v┬▓/(254 x (f + G)). Here, s is the stopping distance, v is the speed of the car, t is the perception-reaction time, G is the grade of the road, f is the coefficient of friction between the tires and the road.

4. Define braking distance?

Braking distance is the distance a vehicle will travel from the point when its brakes are completely applied to when it comes to a complete stop position. It affects the actual speed of the vehicle and coefficient friction between the tires and the road surface.