We cannot determined the measures of water with your pool regarding with the information you provided. Please indicate the exact size of your pool, you said it was 15 ft above ground level and how about the total length and the width of your pool?
6015.77 gallons
319.2 gallons for every inch the water in it is deep.
13,346 gallons per vertical foot.
(18 x 48) / 7.48=115.5
18,000
18,506 U.S. gallons
10053.82 gallons (US) 8371.568 gallons (UK)
An 18x54 above ground round pool typically holds around 7,646 gallons of water when filled to the recommended level.
How large is the pool? In ground or above ground? Shape? Above ground is easier to calculate. I have an oval above ground pool which is 18 x 38. It holds approx. 15,000 gallons. To get an accurate answer, you need to be far more specific.
6015.77 gallons
319.2 gallons for every inch the water in it is deep.
Just a little over 6,000 gallons.
13,346 gallons per vertical foot.
(18 x 48) / 7.48=115.5
5300 Gal
18,000
A round pool that is 16 feet across and is filled with 48 inches of water will contain about 6,041 gallons of water.