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.
Approximately 4,400 gallons.
it also depends how wide it is
17,953.2 gallons
615,142 gallons of water are needed to fill this cylinder.
It will take 5,104.1 gallons of water to fill this cylinder.
If this is a round pool 18 feet across and you fill it with 4 feet of water, it contains 7,646 gallons of water.
It would require 2,937.6 US gallons of water to fill the pipe.
An 18-foot round pool with 3 feet of water contains 5,734.8 gallons of water. If you fill it to 4 feet deep it increases to 7,646 gallons of water.
A pool this size with an average depth of 16 feet requires 462,560 gallons of water to fill it to the top.
If you fill it with 4 feet of water (48 inches), the pool will contain about 5,310 gallons of water.
1795 gallons, if you fill it to the brim.
Three feet of water in a 12-foot round pool is about 2,550 gallons.
4,625.6 gallons.
(3.5 feet) * PI * ((9 feet)^2) = 6 662.46122 US gallons