One ounce is 28.35 grams. NIST lists the avoirdupois ounce as 28.34952 g, so ounces × 28.35 gives grams, and grams ÷ 28.35 gives ounces. For example, 4 oz is 113.4 g, and 100 g is 3.53 oz. This is the ounce used for food, mail and body weight; gold uses a heavier troy ounce.
How many grams are in an ounce?
The avoirdupois ounce is 1/16 of a pound, and NIST's conversion factors (SP 811, Appendix B.8) give it as 28.34952 grams, or 0.02834952 kg. For US nutrition labels the rule differs: 21 CFR 101.9(b)(5)(viii) states that 1 oz in weight means 28 g. The label value is about 1.2% lower (28 ÷ 28.34952 = 0.988), which is why a "1 oz (28 g)" serving is not exactly one ounce.
Formulas
grams = ounces × 28.35
ounces = grams ÷ 28.35
The factor 28.35 is accurate to about 0.01%. For mental math, 30 is easy but runs 5.8% high, so 3 oz as "90 g" is really 85 g.
Ounces to grams chart
| Ounces | Grams |
|---|---|
| 1/4 oz | 7.09 |
| 1/2 oz | 14.17 |
| 1 oz | 28.35 |
| 2 oz | 56.70 |
| 3 oz | 85.05 |
| 4 oz (1/4 lb) | 113.40 |
| 6 oz | 170.10 |
| 8 oz (1/2 lb) | 226.80 |
| 12 oz (3/4 lb) | 340.19 |
| 16 oz (1 lb) | 453.59 |
The converters oz to grams and grams to ounces take any value; pounds to grams and oz to kg cover the bigger steps.
Grams to ounces chart
| Grams | Ounces |
|---|---|
| 10 g | 0.35 |
| 25 g | 0.88 |
| 50 g | 1.76 |
| 100 g | 3.53 |
| 150 g | 5.29 |
| 200 g | 7.05 |
| 250 g | 8.82 |
| 500 g | 17.64 |
| 1,000 g (1 kg) | 35.27 |
Worked examples
Example 1: a recipe in grams
A recipe calls for 250 g of butter. 250 ÷ 28.34952 = 8.82 oz, a little under half a pound (8 oz = 226.8 g).
Example 2: a recipe in ounces
A recipe asks for 6 oz of chocolate. 6 × 28.34952 = 170.1 g. Using the label figure of 28 g per ounce would give 168 g, a gap of 2.1 g.
Example 3: portions from a bag
A 500 g bag of pasta split into 2 oz portions: 2 oz = 56.7 g, and 500 ÷ 56.7 = 8.8 portions, so 8 full portions with 46.4 g left (500 − 8 × 56.7).
Example 4: label serving to grams
A serving size listed as 3 oz weighs 3 × 28.35 = 85.05 g by the exact factor. Under the FDA rounding of 28 g per ounce, the same 3 oz is stated as 84 g.
Example 5: a pound in grams
A pound is 16 × 28.34952 = 453.59 g. So 2 lb is 907.18 g, and 1 kg is 35.27 oz or 2.205 lb. The kg to lbs converter does the larger conversions.
What is a troy ounce in grams?
A troy ounce is 31.10348 g according to NIST, used for precious metals such as gold and silver. The ratio to the food ounce is 31.10348 ÷ 28.34952 = 1.097, so a troy ounce is about 9.7% heavier. A 1 troy ounce coin weighs 31.10 g, not 28.35 g, and treating them as the same would be a 2.75 g error per ounce.
Can fluid ounces be converted to grams?
Not directly. A fluid ounce is a volume of 29.57353 mL, while a gram is a mass. The conversion needs the density: water at about 1 g/mL gives roughly 29.6 g per fluid ounce, but oil and honey give different numbers. The guide to ounces in a cup explains the difference, and cups to grams lists ingredients one by one. Ounces in pounds are covered in how many ounces in a pound.
Quick ways to remember
- 1 oz is about 28 g and 1 lb is about 454 g.
- A quarter pound is 4 oz, about 113 g.
- Round to 28 only for rough work: for baking, use 28.35 or a scale that switches units. The metric vs imperial guide explains how the two systems relate.