To calculate the weights, first determine the contents of the balls in cubic inches, and then multiply by '26. To find the contents of a sphere or ball in cubic inches, cube the diameter in inches (that is, multiply it by itself, and then the product by itself), and multiply by •526C). Thus, the contents of a 7-in. ball equals 7 x 7 x 7 x '526 = 179.6 cub. in., and the weight of the ball is 179.6 x .26 = 46.8 lb. The weight of cast iron per cubic inch varies from .251b. to .271b. A simpler method of determining the weight in pounds is to cube the diameter in inches, and then multiply by .136.