Ounces to Grams

The ounce on this page is the avoirdupois ounce, a sixteenth of a pound. Since the 1959 international yard and pound agreement fixed the pound at 0.45359237 kg, the ounce is exactly 28.349523125 g. It is used for food, postage and almost everything else that is weighed in the US.

The troy ounce is a different unit used only for precious metals. It weighs 31.1034768 g, almost 10% more, so the price of an ounce of gold refers to 31.1 g, not 28.3 g. The fluid ounce is a volume, not a weight: a US fluid ounce is 29.5735 mL and an imperial fluid ounce 28.4131 mL. Only for water and similar liquids does a fluid ounce weigh close to an ounce.

US packaged food shows both units on the label, so a 12 oz bag of coffee is 340 g and a 16 oz box of pasta is 454 g. American recipes give cheese, chocolate and meat in ounces: 8 oz of cream cheese, one standard block, is 227 g, and a 6 oz steak is 170 g. A soda can labeled 12 fl oz holds 355 mL; that figure describes volume, and the full can weighs more than 12 ounces once the aluminum is included.

The US Postal Service prices letters by the ounce. A first-class letter can weigh up to 3.5 oz, which is 99.2 g, and a single sheet of paper in an envelope stays under 1 oz, or 28.3 g. Boxing and sparring gloves are sold by weight too: 16 oz gloves are 454 g each.

For rough kitchen work, 30 g per ounce is close enough: 5 oz becomes 150 g against the exact 141.7 g. For baking, where a few grams matter, use 28.35. The mistake to avoid is converting a fluid-ounce volume as if it were weight; honey or syrup measured as 8 fl oz weighs far more than 227 g. For the reverse direction see grams to ounces, and for pounds and kilograms the unit converter.