For example, a box of clothing shipped internationally which weighs 10 pounds and measures 18 × 18 × 18 inches would be charged as if it weighed 36 pounds: (18 x 18 x 18)/166 = 35.1 pounds which is then rounded up to 36 pounds for shipping cost purposes. The 35.1 pounds is the 'theoretical" weight of the package if it had a density of 166 in3/lb or 10.4 lb/ft3: (18 × 18 × 18) = 3.375 ft3 × 10.4 lb/ft3 = 35.1 lb.