What is the capacity of a bathtub?

My tub (a standard tub by all appearances) is approximately 54" long by 24" wide by 8" deep to the bottom of the overflow. Ignoring the curved corners, that's about 10,368 cubic inches or 44.9 gallons. I could adjust the calculation taking into account that the outside corners are rounded on a 6" radius. Subtract 12x12x8 (1152) and add 3.14*6^2*8 (905). I get 10,121 cu in for 43.8 gallons. I could probably do something about the 3" radius on the bottom perimeter, too, but it should only take away about another 1/2 gallon or so.