Standard vs. troy: the distinction that changes the answer
Both are called “ounces.” They are not the same unit, and neither value is an approximation. Both are fixed exactly by definition. Just need to know which one applies to you? The full comparison settles it in a table.
The everyday ounce
28.349523125 g
Exact: 1⁄16 lb, 1959 agreement
Used for cooking, groceries, body weight, postage, and shipping. Does a recipe or label just say “oz”? Then this is the one it means.
The precious-metals ounce
31.1034768 g
Exact: 480 grains
Used for gold, silver, platinum, palladium, and gemstones. Spot prices, coin listings, and bar weights are always quoted per troy ounce. That is 9.71% heavier than a standard ounce.
Where these numbers come from. The 1959 international yard and pound agreement sets the pound at exactly 0.45359237 kg. That fixes the standard ounce at exactly 28.349523125 g. The grain is exactly 64.79891 mg, and a troy ounce is 480 grains. That gives 31.1034768 g. Nothing here is rounded at the source. Rounding happens only on screen, and you can turn it off. Full methodology →
How far apart the two ounces get
The same number of ounces, read both ways. On one spice jar the difference is a rounding error. On a bullion order it is most of a kilogram.
| Ounces | If standard | If troy | You would be out by |
|---|---|---|---|
| 1 oz | 28.35 g | 31.1 g | 2.75 g |
| 2 oz | 56.7 g | 62.21 g | 5.51 g |
| 5 oz | 141.75 g | 155.52 g | 13.77 g |
| 10 oz | 283.5 g | 311.03 g | 27.54 g |
| 25 oz | 708.74 g | 777.59 g | 68.85 g |
| 50 oz | 1,417.48 g | 1,555.17 g | 137.7 g |
| 100 oz | 2,834.95 g | 3,110.35 g | 275.4 g |
| 250 oz | 7,087.38 g | 7,775.87 g | 688.49 g |
| 500 oz | 14,174.76 g | 15,551.74 g | 1.38 kg |
| 1,000 oz | 28,349.52 g | 31,103.48 g | 2.75 kg |
Common ounce amounts, converted
The amounts people look up most. Each shows the standard reading first and the troy reading beneath, because the same number of ounces gives two different weights. Tap any card to load it into the converter above.
Going the other way? Grams to ounces has the same set for gram amounts, and the full chart covers everything in between.
What these weights actually feel like
A number is hard to picture. Tap anything here to load its weight into the converter above, and read it in both ounces.
Under 10 grams
10 to 100 grams
100 grams to a kilo
Over a kilo
Masses are the real masses of the objects named, so the arithmetic stays honest. They are chosen per language, because a comparison only helps if you have held the thing.
In the kitchen: an ounce of weight is not a fluid ounce
Recipes written in ounces mean weight. They always mean the standard ounce, never the troy one. A fluid ounce is different again: it measures volume. The two only match for water. That is why a cup of flour and a cup of honey weigh such different amounts.
“One cup” is not one measurement either. A US cup is 236.588 ml. A metric cup is 250 ml, used in the UK, Australia, New Zealand, and Canada. A Japanese cup is 200 ml. Australian tablespoons hold 20 ml where everyone else uses 15 ml. So we store density in grams per millilitre and work out every measure from that. The numbers stay right whichever kitchen you are standing in. Ingredient weights and cup systems →
Go deeper
Troy ounce vs ounce
Why two ounces exist, where each is used, and how to tell which a listing means.
CookingOunces to grams for recipes
Ingredient weights by density, cup systems by country, and whole-recipe conversion.
ReverseGrams to ounces
The other direction, with the amounts people look up most called out.
ReferencePrintable oz to gram chart
Standard, troy, kilograms, and pounds on one sheet built to print cleanly.
Frequently asked
How many grams are in an ounce?
A standard (avoirdupois) ounce is exactly 28.349523125 grams, usually rounded to 28.35 g. A troy ounce, used for precious metals, is exactly 31.1034768 grams. If you are weighing gold or silver, the rounded 28 g figure is wrong by about 2.75 g per ounce.
Is 1 oz always 28 grams?
Not exactly. One standard ounce is 28.349523125 grams, so 28 g is a rounding that loses about a third of a gram. For cooking that rarely matters. For anything weighed precisely it does, and for precious metals the answer is not 28 g at all but 31.1034768 g, because those use the troy ounce.
What does oz stand for?
Oz is the abbreviation for ounce. It comes from the Italian onza. There is no difference between "oz" and "ounce" as units. The distinction that does matter is between the standard ounce and the troy ounce, which are different weights sharing the same name.
Is a fluid ounce the same as a weight ounce?
No. A fluid ounce measures volume; an ounce measures mass. They coincide only for water, which weighs almost exactly 1 oz per US fluid ounce. Oils, syrups, and flour do not, so a fluid ounce of honey weighs about 1.4 weight ounces.
How many grams is half an ounce?
Half a standard ounce is 14.1747615625 grams, usually written as 14.17 g. A quarter ounce is 7.0873807813 grams, and an eighth is 3.5436903906 grams.
How many grams are in a pound?
One pound is 16 standard ounces, or exactly 453.59237 grams. A troy pound is a different unit entirely: 12 troy ounces, or 373.2417216 grams, which makes it lighter than an ordinary pound despite the troy ounce being heavier.
What is the formula to convert ounces to grams by hand?
Multiply the ounce figure by 28.349523125 for standard ounces, or by 31.1034768 for troy ounces. To go from grams back to ounces, divide by the same factor. For a rough mental estimate, multiply by 28 and add a little.
Do recipes use standard or troy ounces?
Always standard. Troy ounces apply only to precious metals and gemstones. Any ounce in a recipe, on a nutrition label, or on packaging is a standard avoirdupois ounce of 28.349523125 grams.