This cylindrical tank capacity formula helps you calculate the storage capacity in the U.S. gallons. Gallon is a unit of measurement of the volume of liquids. Gallons unit is differentiated into U.S. gallons and Imperial gallon (UK). To determine the storage capacity for a cylindrical tank in gallons, first, you need to find the volume in cubic inches and then convert it into gallons by substituting the cubic inches values in the tank volume formula gallons.