What are the dimensions of a one-gallon tank?

There is literally an infinite number of tank configurations. If the tank is a sphere, however, there is only one that will hold precisely one gallon. Similarly, there is only one perfect cube that will hold one gallon. Since one gallon is equal to 231 cubic inches, a cube that measures

231(1/3) (the cubed root of 231) inches on each edge will do the trick. That's 6.136 inches. How about the sphere? The volume of a sphere is (4/3)(Pi)r3. Solving for r we get r = 3.81 inches. So, the diameter is 7.61 inches.