If one ignores air friction, the actual acceleration is a constant, 9.8m/s^2.

Now if you are experimenting, and actually trying to measure it, you need a method of plotting distance fell versus time. I have done it with photography in the dark, with a timed light (stroboscope) to give images at selected times.

http://www.edumedia.fr/a217_l2-free-fall-1.html

how do you calculate the acceleration of a free falling object?