Stopping Distance Calculator

How is Stopping Distance Calculated?

Stopping distance depends on several factors including the vehicle's speed, the driver's reaction time, the road grade, and the road conditions. The formula used to calculate stopping distance is:

• SD = Stopping Distance


• Speed = Speed (in meters per second squared)


• RCF = Road Condition Factor (for wet roads this is .45 and for dry roads this is 1)


• RG = Road Grade, or slope

Understanding Your Results

Your result is the distance your car would travel before it comes to a complete stop, taking into account your reaction time and the road conditions. This is important for safe driving, as it gives you an idea of how far you need to stop in different scenarios.

For your convenience, we have included a simple dropdown menu for you to change the unit of length measurement of your answer which will also automatically convert your answer to that new value.

How to Use the Stopping Distance Tool

If you are trying to calculate the stopping distance for a vehicle you are in the right place. It can easily be done with a tool like this. The steps include:

1. Enter the vehicle's speed. Select the proper unit of speed measurement if mph is not correct for you.


2. Enter the approximate reaction time that the driver will have. This will essentially be the time it takes the driver to realize they will need to start to brake.


3. Enter the road grade, or the slope of the road the vehicle is on. This is a percent value where a positive value represents an uphill slope and a negative percent represents a downhill slope. NOTE: The number you enter must be between -40 and 40 because the steepest roads in the world have a slope that is slightly less than that.


4. Use the dropdown selector to choose the current road condition, either dry or wet.


5. Hit calculate and get your stopping distance result in less than a second!

Example Calculation

Let's say you are going on a road trip. You are driving at a rate of 50 miles per hour on a slightly uphill road on a sunny day. You realize a deer is about to run into the road and have to stop as quick as possible. It takes you 2 seconds to begin to break, just how far will the stopping distance be? If we plug 50 into the vehicle speed field, then 2 into the reaction time field and estimate that the road slope was about 15% so we enter 15 in road slope. The road condition is set to dry by default so we do not need to change that.

We are now ready to hit calculate and get our result, after doing so we see that the stopping distance of the vehicle in that situation is approximately 219.31 feet! If we were to be on a wet road the stopping distance would be around 308.11 feet instead.