There are about 7 .5 gallons in a cubic foot of water.
Each fish should have about 100 gallons or more of water.
5.9 x Diameter (feet) x Diameter (feet) x Height (feet) GALLONS
Example, a 2 foot diameter and 18 inches deep tub will contain:
5.9 x 2 x 2 x 1.5 = 35.4 gallons. This is a 1 small fish tub!
7.5 x Width (feet) x Length (feet) x Depth (feet) GALLONS
example: 3 ft. Wide, 5 ft. long, 30 inches deep rectangular pond
7.5 x 3 ft. x 5 ft. x 2.5 ft. = 281 gallons
281 / 100 = about3 fish
An irregular pond will have to be estimated.! It will be less than the rectangular pond it fits into.