How many grams in an ounce? The exact 28.35 g figure

Nutrition labels, kitchen scales, and shipping forms all use “oz,” and the conversion is exact even though it doesn’t look it: 1 avoirdupois ounce equals 28.349523125 grams. Every gram figure on a US food label is calculated from this factor — the number is precise to nine decimal places by international definition, not a rounded estimate.

Where 28.349523125 comes from

The avoirdupois ounce is defined as 1/16 of the avoirdupois pound. In 1959, the United States and several other English-speaking countries signed the international yard-and-pound agreement, fixing the pound at exactly 0.45359237 kilograms. Divide by 16:

0.45359237 kg ÷ 16 = 0.028349523125 kg = 28.349523125 g

Because 0.45359237 is an exact, internationally agreed figure, so is the ounce derived from it — there's no rounding anywhere in the chain. You can read the full definition in NIST Handbook 44, the US federal reference for weights and measures.

Avoirdupois vs troy: not the same ounce

There are two ounces in common use, and confusing them matters for anything valuable. The avoirdupois ounce (28.349523125 g) is the everyday one — food, body weight, postage, most retail goods. The troy ounce(exactly 31.1034768 g) is used almost exclusively for precious metals: gold, silver, platinum. A troy ounce is about 9.7% heavier than an avoirdupois ounce, so a gold price quoted “per ounce” always means the troy ounce, never the kitchen one.

Ounces vs pounds vs grams vs kilograms

The avoirdupois system nests the same way the metric system does, just with different multiples. There are exactly 16 ounces in a pound (7,000 grains, if you trace it back further), and a pound is exactly 0.45359237 kg. That means a kitchen scale toggling between “g” and “oz” modes is really just applying the same 0.028349523125 kg-per-ounce factor in each direction — there's no separate, independently-defined “ounce” unit floating outside the pound's definition, which is part of why the US never fully standardized weight measures against a cleaner base-10 system the way the metric world did.

Reference table: grams to ounces

For a fast mental estimate, multiply grams by 0.035, or divide by 28. Neither shortcut replaces the exact figure for food-label serving sizes or postal weight brackets, where a grams-to-ounces converter applying 28.349523125 g directly is the safer choice.