How to Convert Ounces to Grams (and Back)
Ounces and grams are both units for measuring small weights, but they come from different measurement traditions. US food labels, recipes, and postal scales use ounces. The rest of the world uses grams. This guide explains the exact conversion, clarifies the avoirdupois vs troy ounce distinction, and gives you a practical food weight reference.
Which Ounce Are We Talking About?
There are two ounces in common use, and they are not equal.
The avoirdupois ounce (oz) is the everyday ounce used for food, body weight, and general measurement. 1 avoirdupois ounce = 28.3495 grams. This is the ounce on your kitchen scale and US food labels.
The troy ounce (oz t) is used exclusively for precious metals — gold, silver, platinum. 1 troy ounce = 31.1035 grams, about 10% heavier than the avoirdupois ounce. When a jeweler or commodity market quotes a price per ounce, they always mean troy ounces.
Unless you are dealing with precious metals, you are working with avoirdupois ounces.
The Conversion Formula
1 avoirdupois ounce = 28.3495 grams.
To convert ounces to grams: multiply by 28.3495. For example, 4 oz × 28.3495 = 113.4 g.
To convert grams to ounces: divide by 28.3495 (or multiply by 0.035274). For example, 250 g ÷ 28.3495 = 8.82 oz.
Mental shortcut: multiply ounces by 28 for a quick estimate. The result is about 1.2% low — fine for casual use.
Common Food Weight Conversions
Everyday reference values:
- 1 oz = 28.35 g (one slice of bread)
- 2 oz = 56.7 g (small chicken breast portion)
- 4 oz = 113.4 g (quarter pound)
- 8 oz = 226.8 g (half pound)
- 16 oz = 453.6 g (1 pound)
- 100 g = 3.53 oz
- 200 g = 7.05 oz
- 500 g = 17.64 oz (about 1.1 lb)
US Food Labels and Serving Sizes
US food labels show weight in both ounces and grams. A can of tuna labeled "5 oz (142g)" uses the avoirdupois ounce. The grams figure is the authoritative measurement — the oz value is rounded.
Cereal boxes, snack bags, and deli counters in the US use ounces. European products use grams. When adapting a recipe from one system to the other, use the exact conversion factor for baking — rounding to 28 g per oz can introduce measurable error over large quantities.
Cooking and Baking Reference
Key ingredient conversions (1 oz = 28.35 g):
- 1 oz all-purpose flour ≈ 28 g
- 1 oz granulated sugar ≈ 28 g
- 1 oz butter ≈ 28 g
- 1 oz cream cheese ≈ 28 g
- 1 oz chocolate ≈ 28 g
- 1 oz shredded cheese ≈ 28 g
Conclusion
1 avoirdupois ounce = 28.3495 grams. For precious metals, 1 troy ounce = 31.1035 grams. For everyday cooking and food weights, multiply ounces by 28.35 or divide grams by 28.35. Use our free weight converter for precise results in both directions.