When you say 18 ft round, does that mean 18 feet diameter, radius, or circumference?
I am going to assume its the diameter. The radius is half the diameter (9 ft from the center).
pi * radius * radius is the area of the pool.
3.14 * 9 * 9 = 254.34 cubic feet of space in your pool.
A quick search on Google says one cubic foot is equivelent to 7.48 gallons of liquid.
Therefore 254.34 cubic feet * 7.48 gallons is 1902.46.
Your pool will take 1902.46 gallons to fill to the top. If your pool has a radius of 18 feet then replace 9 with 18 and do the calculations over again. If its circumference then replace 9 with 2.87. I highly doubt a pool would be 5 feet wide and 4 feet deep, but hey if that's what you got then that's the number you'll need to use. Hope this helps.
Answeron must also include the debth of 4'. So multiply your answer by 4About 18,402 gallons.
About 24 gallons.
13,594 US gallons of water.
1,770 gallons.
3384 gallons for every foot deep it is.
A 2-foot round pool with 12 inches of water is holding about 23.6 gallons of water.
This pool holds a maximum of about 10,360 gallons of water.
About 5,310 gallons.
26,550 gallons.
9,440 gallons.
2,360 gallons.
17,204 gallons.