What is a Ounce?

The ounce equals exactly 28.349523125 grams or 1/16 of a pound. The word derives from the Latin 'uncia,' meaning one twelfth (the original Roman ounce was 1/12 of a Roman pound). The modern avoirdupois ounce, used for everyday weights in the United States and the United Kingdom, replaced the older Tower and Troy systems. It is the standard unit for American kitchen recipes (where 'ounce' refers to weight, distinct from the fluid ounce of volume), postal rates, package sizes (a 12-oz can of soda), and boxing-glove weights. Precious metals like gold and silver use the troy ounce (31.103 g), about 10% heavier than the avoirdupois ounce. The ounce relates to the pound (16 oz = 1 lb), the gram (1 oz ≈ 28.35 g), and the grain (1 oz = 437.5 grains).

Visual reference for how the ounce relates to other weight units. Each row links to the full converter for that pair.

• American and British cooking recipes
• Food packaging in the US
• Precious metals (troy ounce = 31.10 g, different from avoirdupois)

• ✓1 oz = 28.35 g exactly (avoirdupois); 1 troy oz = 31.10 g.
• ✓16 oz = 1 lb in the avoirdupois system used for food.
• ✓When converting a US recipe, 1 oz ≈ 2 tablespoons of a liquid ingredient.

• ✗Confusing mass ounces (28.35 g) with fluid ounces (volume).
• ✗Using avoirdupois ounces (28.35 g) for precious-metal pricing — gold is in troy ounces (31.10 g).
• ✗Multiplying lb × 16 and calling the result oz — correct only for weight, not volume.