Acceleration is the derivative of velocity, so it is a measure of the change in velocity over time. Dimensional units reflect this as fps (feet per second) for velocity and fps^2 (fps per second). Here, acceleration is simply given as the change in velocity divided by the time. [tex] \frac{Vfinal - Vinitial}{time} = acceleration[/tex]
This works as long as all your units are equivalent (i.e. if time was in minutes and velocity was in f/s, you would need to convert first).