Volume by rings, also known as volume by disks or volume by washers (if the area between two functions is being rotated around an axis), is a method of finding the volume of a solid of revolution. This method involves splitting the shape into indefinitely small circular rings. The formula for the volume of any solid of rotation is or , depending on which axis the rotation is around. In the case of volume by rings, the formula is or assuming the rotation is around the x-axis. If the rotation is of an area between two functions, the formula is