Is a fluid ounce the same as an ounce?

No, and confusing them ruins recipes. An ounce is mass, a fluid ounce is volume. They coincide only for water by rough coincidence; for flour or honey the numbers are far apart.

How many grams in a cup?

That depends entirely on the ingredient, because a cup measures volume. A cup of water is about 237 grams, a cup of flour roughly 120 grams. This is why weighing beats measuring by cup for baking.

Why do tables show 28.35 grams?

It is the exact value rounded. NIST publishes 2.834 952 E+01 grams per ounce, seven significant digits, while the underlying definition gives 28.349523125 exactly. This tool computes with the exact value and checks itself against the published one.

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Grams to Ounces

Convert grams to ounces for recipes and postage. One avoirdupois ounce is a sixteenth of a pound, which works out at 28.349523125 grams exactly.

oz = g ÷ 28.349523125

NIST SP 811 (2008), Appendix B.8 — ounce (avoirdupois) (oz) to gram (g) = 2.834 952 E+01

Recipes are where grams and ounces collide most often, and where the difference between a weight ounce and a fluid ounce causes the most trouble. This converter handles mass only: an ounce here is a sixteenth of a pound, exactly 28.349523125 grams. A fluid ounce measures volume and depends on what you are pouring.

How it is calculated

oz = g ÷ 28.349523125

The exact value comes from the definition of the pound divided by sixteen. Published tables often round it to 28.34952, which is accurate to seven digits and perfectly adequate in the kitchen.

Source: NIST SP 811 (2008), Appendix B.8 — ounce (avoirdupois) (oz) to gram (g) = 2.834 952 E+01

Common values

grams	ounces
1	0.035273962
10	0.35273962
25	0.88184905
50	1.7636981
100	3.5273962
125	4.4092452
200	7.0547924
250	8.8184905
500	17.636981
1,000	35.273962

Questions people ask

Is a fluid ounce the same as an ounce?: No, and confusing them ruins recipes. An ounce is mass, a fluid ounce is volume. They coincide only for water by rough coincidence; for flour or honey the numbers are far apart.
How many grams in a cup?: That depends entirely on the ingredient, because a cup measures volume. A cup of water is about 237 grams, a cup of flour roughly 120 grams. This is why weighing beats measuring by cup for baking.
Why do tables show 28.35 grams?: It is the exact value rounded. NIST publishes 2.834 952 E+01 grams per ounce, seven significant digits, while the underlying definition gives 28.349523125 exactly. This tool computes with the exact value and checks itself against the published one.

Found a problem, or want more?

A number that disagrees with its source is a defect, not a rounding preference.

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