How to use the skid mark speed calculator
Estimate a car speed before braking from the length of its skid marks. Enter skid length, tyre friction coefficient in the fields above; the initial speed are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “speed from skid marks”, “how fast was the car”, “accident speed estimate”, “calculate skid mark speed”, “find initial speed”.
Formula
Variables
- d — Skid length (m)
- mu — Tyre friction coefficient
Worked example
With skid length = 40 m, tyre friction coefficient = 0.7, the calculator gives initial speed ≈ 23.43443 m/s; initial speed ≈ 84.36394 km/h.
Frequently asked questions
What is the skid mark speed calculator used for?
Estimate a car speed before braking from the length of its skid marks. It helps with questions such as “speed from skid marks”, “how fast was the car”, “accident speed estimate”.
What is the formula for the skid mark speed calculation?
Initial speed (m/s) = √(2 × mu × GRAV × d). Initial speed (km/h) = [Initial speed] × 3.6. Here d is skid length (m), mu is tyre friction coefficient.
What inputs do I need for the skid mark speed calculator?
You need skid length in m, tyre friction coefficient. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the skid mark speed calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the skid mark speed result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.