I dont know exactly what you used to calculate the gallons but that number isnt even close. THe formula for a round pool would be 3.14 x r x r x AD x 7.5 Where r is the radius and AD is the average depth. So for this pool it would be 3.14 x 7.5 x 7.5 x 3 x 7.5 which would give you 3,974