A cylinder is a geometrical shape that has circles as the top and bottom bases. The cylinder length (height) corresponds to the top to bottom distance. The volume of a cylinder is obtained by multiplying the length of the cylinder by the square of the radius of the circle base, multiplied by pi, the mathematical constant used to calculate the area within a circle. You can also use this formula to calculate the volume of many objects of a cylindrical shape; for instance, the volume of a round swimming pool.
Measure or get elsewhere the diameter of the cylinder.
Divide the diameter by two to compute the radius of the cylinder. For example, if the diameter is 2.2 feet then the cylinder radius is 2.2 / 2 = 1.1 feet.
Raise the radius to the second power (multiply it by itself), and then multiply by the mathematical constant pi (3.1416) to calculate the area of the cylinder base. In the example, the area will be 1.1 x 1.1 x 3.1416 = 3.801 square feet.
Measure or get elsewhere the cylinder length. For example, the cylinder length is 5.5 feet.
Multiply the base area of the cylinder by its length to calculate the volume. In our example, the volume is 3.801 square feet x 5.5 feet = 20.9055 cubic feet.
Multiply the cylinder volume in cubic feet by 7.4805 to calculate it in gallons. In the example, the cylinder volume is 20.9055 x 7.4805 = 156.3836 gallons.
If you calculated the volume of the cylinder in cubic meters, then multiply the value by 264.172 to get gallons.