Article — Ounces to Grams Converter
Ounces to grams: convert oz to g exactly
One avoirdupois ounce equals exactly 28.349523125 grams — the value you get by dividing the international pound (453.59237 g) by 16. One troy ounce, used only for precious metals, equals 31.1034768 grams. Knowing which ounce someone is talking about matters: the troy ounce is 9.7% heavier, and a gold quote using the wrong one is wrong by roughly $200 per ounce at current prices.
The calculator at the top of this page handles both ounce types and converts in either direction. The article below covers when to use which, where the numbers come from, and the common traps.
What is an ounce?
An ounce is a unit of mass. The trouble is that there are two — the avoirdupois ounce and the troy ounce — and they look identical on the page. In modern use, the avoirdupois ounce dominates. It is what your kitchen scale measures, what the post office charges by, and what shows up on nutrition labels. The troy ounce survives only in precious-metals trading.
The word "ounce" comes from the Latin uncia, meaning "one-twelfth" — originally one-twelfth of a Roman pound. The English avoirdupois system reset the ratio: one English pound contains 16 ounces rather than 12. The 1959 International Yard and Pound Agreement then fixed the avoirdupois pound at exactly 453.59237 grams, which fixes the ounce at exactly 28.349523125 g.
The oz to grams formula
To convert ounces to grams, multiply by 28.349523125. To go the other way, divide by the same number:
g = oz × 28.3495 (avoirdupois)oz = g ÷ 28.3495 (avoirdupois)g = oz × 31.1035 (troy)oz × 28 (mental math, ~1.2% off)The factor is exact, not measured. Any calculator that uses more than nine decimal places is rounding an irrational tail beyond practical use. Six decimals is enough for laboratory work; two is enough for cooking.
Common ounce conversions
The most-searched values, at the exact avoirdupois factor:
- 1 oz = 28.35 g (a slice of cheese)
- 2 oz = 56.70 g
- 4 oz = 113.40 g (a quarter pound, raw burger patty)
- 6 oz = 170.10 g (a typical chicken breast)
- 8 oz = 226.80 g (half a pound)
- 12 oz = 340.19 g (a US soda can)
- 16 oz = 453.59 g (one full pound)
- 32 oz = 907.18 g (two pounds, near a kilogram)
Avoirdupois vs. troy ounce
The two ounces differ by 9.7%. That gap quietly produces some of the most expensive misunderstandings in commerce:
The word "troy" has nothing to do with ancient Troy. It comes from Troyes, a French city in the Champagne region that hosted Europe's biggest medieval trade fairs starting in the 12th century. Merchants standardised the troy ounce there for weighing gold, silver, and spices. The fairs faded by the 14th century. The unit they invented is still the standard on every gold exchange in the world.
Ounces in cooking
US recipes use the avoirdupois ounce. A "4 oz" portion of chicken weighs 113 grams. A "1 oz" measure of cheese weighs 28 grams. Restaurant portion control runs on these values.
European recipes are almost always in grams, which is more precise. American cooks who switch to gram-based recipes notice that their bakes become more consistent — a 200-gram flour measurement is reproducible to within a gram, while "1.5 cups" of flour varies by 20 grams depending on how packed the cup is.
For baking, buy a digital kitchen scale and switch from volume to weight. Professional bakeries worldwide weigh ingredients in grams for repeatability. A $20 scale is the single biggest accuracy upgrade home bakers can make.
Oz vs. fl oz: mass versus volume
"Oz" abbreviates two completely different units depending on what is being measured. Oz alone is mass: 28.35 grams. Fl oz is volume: 29.57 mL in the US, 28.41 mL in the UK.
For water at room temperature, the two ounces happen to agree to within a couple of percent. For anything else they do not. One fluid ounce of honey weighs about 1.5 mass ounces. One fluid ounce of vegetable oil weighs about 0.92 mass ounces. Confusing the two has wrecked many a recipe.
When you double a recipe and convert "2 fl oz of olive oil" to grams using the mass-ounce factor, you under-measure by 9%. Read the unit carefully: "fl oz" is volume, plain "oz" is mass. Recipes from cookbooks usually clarify; recipes from internet comments often do not.
Common ounce-to-gram mistakes
Using troy ounces for non-precious-metal weights. If you weigh 4 troy ounces of flour, you have 124 grams instead of 113 — about 10% more than the recipe calls for.
Confusing oz with fl oz. Mass versus volume. They only agree for water. An "8 oz" measure by weight of olive oil is very different from "8 fl oz" by volume.
Rounding to 30 g per ounce. Quick and easy, but 6% high. Fine for casual cooking, wrong for nutrition labels and pharmacy work.
Forgetting the historical context of "ounce" in old recipes. Recipes from before 1959 may use the older US or imperial avoirdupois ounce, which differed from the modern value by a tiny amount. The gap is invisible in practice for cooking, but it can matter in historical metrology or scientific documents.