That will depend on how deep you want the water to be.
You will need a maximum of 11,230 gallons of water.
If you fill it with 4 feet of water (48 inches), the pool will contain about 5,310 gallons of water.
Exactly 5264.1669 gallons
To fill this pool completely with water requires 23,940 US gallons of water.
To fill this pool to a depth of four feet you will need about 7,646 gallons of water. If you decide to fill it to three feet deep, the gallons decreases to around 5,735.
If you fill it to four feet deep, the total is 10,408 gallons of water.
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.
1795 gallons, if you fill it to the brim.
If this is a round pool that is 18 feet across and you fill it to 3 feet deep, the total volume would be about 5,735 gallons of water. Filling it to 4 feet deep will increase the volume 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.
Three feet of water in a 12-foot round pool is about 2,550 gallons.
Alittle under 10,000 gallons.