Multiply the time in seconds that your object has been in free fall by 10 m/s2, an approximation for acceleration due to gravity on Earth. A closer approximation to the actual figure is 9.82 m/s2. This will give you the velocity of your object at a given time since free fall began. For example, after free falling for six seconds, an object has a velocity of (6 s times 10 m/s2) or 60 m/s.
Insert your time value into the equation d = 0.5 g x t2 to determine the distance that the object has fallen during that time. For example, after free falling for six seconds, the object has fallen a distance of (0.5 x 10 m/s2 x 6 s x 6 s) or 180 meters.
Multiply the result by 3.28 ft/m to convert the value from meters to feet.