Just happened to be figuring for an oval shaped pool and noticed my math and pool math doesnt come out the same.

To figure area for an oval shape I use this formula. Say for 1000 by 500 feet oval shape with 10 foot depth.

width radius (250) x length radius (500) x 3.14159265 (pi) = 392699.08125 square feet.

square feet x depth = 3926990.8125 cubic feet.

cubic feet x 7.48 gallons in a cubic foot = 29,373,891.2775 gallons of water in the oval shape.

Pool math shows 33,389,300 gallons of water.

When I calculate for a circle with the same formula with 500 by 500 feet with 10 foot depth I get 14,686,945.6 gallons of water while pool math gets 14,688,000 which would be right or close enough but the oval shape is way off.

Whats wrong here?