Multiply all the numbers to get the volume of the pool in cubic feet. Then divide by 7.5. That assumes the water is filled to a height of four feet. Some above-ground pools have 52" walls, which allow for a water height of 48", which is four feet. The dimensions stated above in the reworded question are for an oval pool, not a round one. I suspect the original question was for a round pool with an 18' diameter and a 4.5' wall. (The slash in 4 1/2 did not show up in the question.) If that is the case, then the answer is 3.14 times 81 times 4.5 divided by 7.5.
How many gallons will fit into a 24 foot diameter x 4 foot high round swimming pool
5284.62 gallons
A round swimming pool 12 feet across by 4 feet deep will hold 452 ft3 which converts to 3,381 gallons
29,555.46 gallons.
18,000
13,346 gallons per vertical foot.
It is 30.6 cubic feet = 190.3 Imperial gallons.
A 12-ft round pool with depth of 2 ft has a capacity of 1,692.2 gallons of water.
There is NO way to calculate this without knowing how deep the pool is filled!
To calculate this the depth would also be needed
10,408 gallons.
13,500 gallons