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How Many Grams in an Ounce? The Exact Number and How to Use It
By How many grams in an ounce? Exactly 28.349523125 grams, or 28.35 grams for most uses. That is the avoirdupois ounce, the one US food labels use for weight. Going the other way, a gram is about 0.035274 ounce. Two other ounces are different sizes: a troy ounce, used for gold and silver, is about 31.10 grams, and a fluid ounce measures volume, not weight. If you sell by weight, such as coffee in custom coffee bags, the label states the weight in ounces, and FDA’s food label rule allows grams beside it.
Where the Exact Number Comes From
NIST, the US measurement agency, gives the pound as exactly 0.45359237 kilogram in its Guide to the SI. A pound is 16 ounces, as FDA’s own label example “Net Wt. 24 oz (1.5 lb)” shows. Dividing 453.59237 grams by 16 gives 28.349523125 grams in one ounce, exactly, which rounds to 28.35 grams for everyday conversions. The common shortcut of 28 grams is about 1.2 percent lighter than the real ounce.
For cannabis weights, see what a quarter of weed weighs.
Three Ounces, Three Sizes
| Ounce | Measures | In metric | Used for |
|---|---|---|---|
| Avoirdupois ounce (oz) | Weight | 28.349523125 g, exact | Weight on US food labels |
| Troy ounce | Weight | 31.10348 g | Gold, silver and platinum |
| US fluid ounce (fl oz) | Volume | 29.57353 mL | Liquid volume on US food labels |
| Imperial fluid ounce | Volume | 28.41306 mL | The UK and Canadian fluid ounce |
Source: NIST’s conversion factors, read in October 2026; the exact avoirdupois figure is computed above.
A troy ounce is about 9.7 percent heavier than an ordinary ounce. NIST’s model rule for selling precious metals, which states can adopt, says that when the price depends on weight, they are sold by troy weight or by metric weight, and when sold in grams, a chart to troy units has to be on display.
Ounces to Grams
| Ounces | Grams |
|---|---|
| 1/4 oz | 7.09 g |
| 1/2 oz | 14.17 g |
| 1 oz | 28.35 g |
| 2 oz | 56.70 g |
| 4 oz | 113.40 g |
| 6 oz | 170.10 g |
| 8 oz | 226.80 g |
| 12 oz | 340.19 g |
| 16 oz (1 lb) | 453.59 g |
| 24 oz (1.5 lb) | 680.39 g |
| 32 oz (2 lb) | 907.18 g |
Grams to Ounces
| Grams | Ounces |
|---|---|
| 28 g | 0.988 oz |
| 50 g | 1.764 oz |
| 100 g | 3.527 oz |
| 250 g | 8.818 oz |
| 500 g | 17.637 oz |
| 1,000 g (1 kg) | 35.274 oz |
Both tables are computed from 28.349523125 g per ounce and rounded only at the end.
How to Convert Without Rounding Errors
NIST’s advice for any unit conversion is to use the exact factor when one exists, and to round only the final answer, not the numbers along the way.
- Ounces to grams: multiply by 28.349523125. For 12 ounces, that gives 340.19 grams, while multiplying by 28 instead gives 336 grams, about 4 grams short.
- Grams to ounces: divide by 28.349523125. For 500 grams, that gives 17.637 ounces, which you can then round to the precision your label or recipe needs.
How a US Food Label States Ounces and Grams
FDA’s net quantity rule, as read in October 2026 (21 CFR 101.7), sets out how weight appears on a US food label:
- Units. Weight is stated in avoirdupois pounds and ounces, the ordinary ounce described above.
- Order. On packages under 4 pounds, ounces come first, and from 1 pound upward the pounds follow in parentheses, as in “Net Wt. 24 oz (1.5 lb)”.
- Fractions. Three quarters of a pound is written as “Net Wt. 12 oz” rather than as a fraction of a pound.
- Weight or volume. FDA says that pairing “Net wt.” with ounces, or writing “fl oz”, is enough to show which ounce is meant.
- Metric. An accurate metric statement in grams may also appear, either on the front panel or on other panels.
Cosmetics follow their own rule on metric figures, covered in our cosmetic label requirements post.
Printing Net Weight on Your Packaging
Printing is CMYK, Pantone or PMS, or unprinted. Send your artwork and we will tell you how it will reproduce on the stock you have picked.
Frequently Asked Questions
How many grams are in an ounce?
Exactly 28.349523125 grams, which rounds to 28.35 grams for everyday conversions and recipes.
How many grams are in a troy ounce?
About 31.10348 grams. Under NIST’s model rule, gold, silver and platinum sold by weight are sold in troy units or in grams.
Is a fluid ounce the same as an ounce of weight?
No. A US fluid ounce measures volume and equals 29.57353 milliliters, while an ounce of weight is 28.349523125 grams.
How many ounces are in 100 grams?
About 3.527 ounces, found by dividing 100 by 28.349523125.
Why do people say 28 grams in an ounce?
It is a convenient rounding, but it sits about 1.2 percent below the exact figure, so larger amounts drift further off.
Anthony Kim
Hello, I'm Anthony Kim, a seasoned packaging consultant and designer. With a professional journey spanning over four years, I've evolved from a budding designer to a recognized expert in the field. Currently holding the position of Packaging Consultant, I've honed my skills in creating not just visually stunning packaging but also solutions that align with strategic business goals.
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