How many gallons of water in standard us swimming pool?

Your average swimming pool is likely around 20 ft x 30 ft with an average depth of 5 ft (rounding here of course) this would equate to about 22,500 Gallons.

1 cubic foot of water = 7.4805 US Gallons

20 x 30 x 5 x 7.4805 = 22,442