Determining Deceleration Using Speed Difference and Time

This is quite simple. First subtract the ending speed from the starting speed.

Convert the speed difference to units of speed that are compatible with the Acceleration to be calculated, usually metre per second. If the speed is in miles per hour, convert that speed to metres per second by multiplying kilometers per hour by 0.278.

Then, divide the speed change from the time during which the change occurred. This calculation gives us the value of the average Deceleration rate.