How many gallons of water are in a 21' x 52' round above-ground swimming pool?
First, figure the surface area. 21 ft diameter is 10.5 foot radius. Convert to inches, since that is easier for me. 10.5 ft is 126 inches. Area is Pi ( about 3.14159) times R squared. So 3.14159 x 126 x 126 = roughly 49,876 square inches. That is the surface area of the bottom of the pool. Now multiply that times the height of the water. I will use 52 inches, though you won't fill it completely up to the rim. 49,876 times 52 = about 2,593,552 cubic inches of water. One gallon of water takes up 231 cubic inches. So divide 2,593,552 by 231, and you get 11, 227.5 gallons. Roughly speaking. Depends on how high you fill it. My 9th grade science teacher, Mrs. Monel, gets the credit for teaching me this method.
It depends on how deep you fill the pool. So, let's take the most common depths for a 33-foot round pool; 3, 4 and 5 feet: For 3 feet of water the total gallons will be about 19,275. For 4 feet of water the total gallons will be about 25,700. For 5 feet of water the total gallons will be about 32,125.
go to www.extendaswim.com and use the pool volume calculator to find out the exact gallons A 24 foot round pool that is 52 inches deep will hold approximately 14,645 gallons of water if filled completely. If filled to a 90% capacity, as recommended by most swimming pool manufacturers, it will hold approximately 12,481 gallons.
Determine how many gallons of water your swimming pool holds. You will also need to consider what size filter that you have. If you have an undersized filter to pump it can create filtration and circulation problems. Be sure to look at the turnover rate for your pump and filter that you are considering. If you have an aboveground pool most pump and filters are sold as a pre-sized set.