The ounce (avoirdupois) is a unit of mass ("weight"). The pound (lb or #) is divided into 16 ounces. One pound is approximately equal to ⁵⁄₁₁ (0.45) kg or 454⁵⁄₁₁ (454.54) g. Therefore, one ounce is approximately equal to ⁵⁄₁₇₆ (0.028409) kg or 28⁹⁄₂₂ (28.409) g. However, the international avoirdupois ounce is equal to 0.45359237⁄16 kg or 28.349523125 g per ounce.
The ounce is herein abbreviated as oz.
Note that the ounce is distinct from the fluid ounce. The troy ounce and apothecaries ounce are not used in cooking.