There are no gallons of water in a square foot. Gallons is a unit of volume, and square feet is a unit of area, not volume. If you are asking about cubic feet, however, the answer is there are about 7.5 gallons in a cubic foot.

30 feet X 15 feet X 4 feet would be (30 X 15 X 4) = 1,800 cubic feet of water. 1 cubic foot of water = 7.48051948 US gallons so 1,800 X 7.48051948 = 13,464.935064 gallons.

I'm assuming you mean acre feet of water. If that is the case, then there are 325,850.58 gallons in one acre foot of water or 4,887,758.7 gallons of water in 15 acre feet of water.

There are about 7.481 gallons per cubic foot. So if your 12 foot by 8 foot pool is filled 4 feet deep you will need 12 x 8 x 4 x 7.481 = 2,873 gallons of water.

There are 7.48 gallons in one cubic foot of liquid water. Your pool's dimensions are 14x48x4 in feet. 14x48x4 = 2488 cubic feet 2488 cubic feet times 7.48 gallons per cubic foot equals 20106.24 gallons in your pool.

There are 13,536 gallons in a 24 foot diameter pool that has 4 feet of water. Not true for a pool that is 4 feet in height. This would hold less than 4 feet of water.