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 4area of a circle equals pi * radius so 3.14 * 9ft * 9ft = 254.34 square ft
254.34 square ft * 4 ft deep = 1017.36 cubic ft
since there are 7.48 gallons in 1 cubic ft of water, multiply 1017.36 * 7.48 = 7609.85 gals of water in the 18 ft round by 4 ft deep pool
If the pool is cylindrical, four feet deep and eighteen feet in diameter the volume is
π × r2 × h cubic feet
3.1416 × 9 × 9 × 4 = 1018 cubic feet
one cubic foot is about 7.48 gallons so:
over 7500 gal
Use this formula: Diameter x Diameter x Average Depth x 5.9 = Total Gallons
This pool can hold up to about 7,615 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.
7,646 US gallons.
About 7,646.4 gallons.
7,614 gallons
32000
About 24 gallons.
About 18,402 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 212 gallons.
About 5,310 gallons.
About 17,204 gallons.
About 13,010 gallons.
17,204 gallons.