Skid Speed Calculator

This calculator is provided without warranty or applicability to any specific situation. Do not use the results of this calculator in any legal proceedings or insurance claims actions. It is not a substitute for a speed analysis by a qualified traffic accident reconstructionist.

Select the surface type.                 
(Default is Asphalt)

Select condition, wet or dry.                   
(Default is Dry)

Enter the grade in percent.*                   %
Use 0 (default) if unknown.
Use negative ( - ) for a downhill skid.
Example: 2.5% downhill = -2.5
Enter the length of the skid.                    feet

The result will appear in a new window. The form will reset to the default values after each calculation.


* Percent value for grade if the angle in degrees is known:
  Level = 0%
  1.0° =  1.74% grade                    
  2.0° =  3.49% grade                 
  3.0° =  5.24% grade              
  4.0° =  6.99% grade                 
  5.0° =  8.74% grade
  6.0° =  10.51% grade
  7.0° =  12.27% grade
  8.0° =  14.05% grade

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All new 2014 and later model year cars, light trucks, vans and SUVs sold in the United States are equipped with an Event Data Recorder.

Typical records include vehicle speed, throttle position, brake application, engine speed and velocity change through the collision. Some vehicles also record steering input angles.

EDRs do not record location, date or time, audio or video, however, many consumer grade automotive GPS units record significant information. This includes, speed, direction, time of day and date.

Determining the speed of a vehicle based on skid marks depends on several variables. These include the "coefficient of friction" of the roadway, tires etc.. 

The presence of water, ice, or snow on the road will also affect the computation, as will the condition of the tires and the grade (slope) of the roadway. In general, a  speed estimate of a vehicle while skidding can be made. Because of other variables listed this calculator only gives a rough estimate of the length of skid.

The answers to your calculations are only an estimate and should be verified by traffic accident experts if you were in an accident. The estimate by accident experts will be different and more accurate that any online calculator. Do not rely on this online calculation only, it is just an estimate example.