Deceleration, or decrease in speed, can be calculated using multiple different formulas, depending on the available parameters. Some deceleration formulas include a = (v - u)/t, and a = (v^2 - u^2) / (2s).
One formula to calculate deceleration is a = (v - u)/t, where a is the deceleration, v is the final velocity, u is initial velocity and t is the time taken. If distance covered is known but time passed is not known, a second formula that can be used is a = (v^2 - u^2) / (2s), where a is the deceleration, v is final velocity, u is initial velocity and s is the distance covered. The deceleration formulas calculate the rate of decrease in overall speed. Deceleration is typically measured in meters per second^2, or other distance per time unit squared units.