Convert ounces to grams

g = oz × 28.349523125

This is the avoirdupois ounce, one sixteenth of a pound. Since 1959 the pound has been defined as exactly 0.45359237 kg, so the ounce is exact too.

Precious metals are priced in troy ounces, which weigh 31.1035 g — about 10% more than an ordinary ounce. When a news report quotes the price of gold "per ounce", it means troy. Converting a gold price with 28.35 instead of 31.10 undervalues the metal by roughly a tenth.

The name ounce comes from the Latin uncia, a twelfth — originally a twelfth of a Roman pound. The troy pound still has twelve ounces; the everyday avoirdupois pound has sixteen.

American recipes weigh in ounces; most of the world weighs in grams. For baking, use the exact figure: a recipe calling for 8 oz of flour is 227 g, and rounding to 25 g per ounce would leave you 27 g short. For savoury cooking, 28 g per ounce is plenty.

Watch for the fluid ounce, which measures volume — 8 fl oz of milk is a cup, not 227 g of anything in particular. That conversion is on oz to mL.

• 1 oz = 28.35 g — a US first-class letter weight step
• 4 oz = 113 g — one US stick of butter
• 12 oz = 340 g — a standard US bag of coffee
• 16 oz = 454 g — one pound

The everyday ounce is the avoirdupois ounce, one sixteenth of the pound. With the pound fixed at 0.45359237 kg by the 1959 agreement, that makes it exactly 28.349523125 g, the value given in NIST Handbook 44 (NIST Special Publication 811, the US guide to the SI rounds it to 28.34952 g). The troy ounce used for precious metals is a different unit, about 31.103 g.