Grams to Ounces

To go from grams to ounces, divide by 28.35: 100 g ÷ 28.35 ≈ 3.53 oz. For the reverse, multiply by 28.35. The exact value of the avoirdupois ounce is 28.349523125 g, and it is exact rather than measured. The 1959 international yard and pound agreement fixed the pound at exactly 0.45359237 kg; divide that by 16 and the ounce falls out with no rounding at all. For cooking, 28.35 is plenty. For labeling, shipping rates and trade, the full factor keeps errors from accumulating across a large count.

This is the most ambiguous unit in everyday American measurement, and the confusion is expensive. Three separate quantities answer to the name. Avoirdupois ounce (oz) — the ordinary weight ounce, 28.35 g. Food, mail, and general use. Troy ounce (ozt) — used only for precious metals, 31.1035 g, about 10% heavier. Gold, silver and platinum are always quoted per troy ounce, never per regular ounce. Converting a metal quote with 28.35 misprices it by roughly 10%. Fluid ounce (fl oz) — which measures volume, not weight. The US fluid ounce is 29.5735 mL and the UK one is 28.4131 mL. It measures a different kind of thing entirely, and it cannot be turned into grams without knowing the density of whatever is in the cup.

English-language recipes use "oz" for both quantities, and only context tells you which. 8 oz of flour is weight, about 227 g. 8 fl oz of milk is volume, about 237 mL. Two letters separate them, and the practical difference is enormous. It gets worse, because the US customary cup is defined as exactly 8 fluid ounces — which leads a lot of people to conclude that "1 cup = 8 oz by weight". That holds only for water, and only by the coincidence that water is about 1 g per mL. A cup of all-purpose flour weighs somewhere around 120 to 125 g, not 227 g — closer to half. The safe rule: if the ingredient is a liquid, "oz" is almost certainly fluid; if it is dry or solid, it is almost certainly weight. And when the result actually has to work — bread, pastry, anything with a leavening ratio — use a scale rather than a measuring cup.

The avoirdupois ounce is 1/16 of a pound, which is why American weights appear in mixed notation: "1 lb 4 oz" is 20 ounces, about 567 g. Deli counters, baby weights and shipping labels all use this form. References worth memorizing: 1 oz = 28.35 g; 4 oz = 113.4 g (the standard restaurant protein portion, and the reason a quarter-pound patty is "4 oz raw"); 8 oz = 226.8 g; 12 oz = 340.2 g; 16 oz = 453.6 g, a full pound. Going the other way: 50 g ≈ 1.76 oz; 100 g ≈ 3.53 oz; 250 g ≈ 8.82 oz; 500 g ≈ 17.64 oz; 1 kg ≈ 35.27 oz. Note that a 12 oz soda can is fluid ounces — 355 mL — and has nothing to do with 340 g.

Every international precious-metal quote is stated per troy ounce. When a market report gives the price of gold "an ounce", that is the unit being used. To turn a quote into a price per gram, divide by 31.1035 — not by 28.35. Using the ordinary ounce overstates the per-gram price by about 10%, which on a real purchase is a serious amount of money. The troy system has one more quirk that catches people out: a troy pound contains 12 troy ounces, not 16. The result is counterintuitive — the troy ounce is heavier than the avoirdupois ounce, yet the troy pound (373.24 g) is lighter than the avoirdupois pound (453.59 g).