The formula
The ounce in US and UK kitchens is the avoirdupois ounce, one sixteenth of a pound. Since 1959 the pound has been defined as exactly 0.45359237 kg, which NIST Handbook 44 lists, so the ounce is exactly 453.59237 / 16 = 28.349523125 g.
ounces = grams / 28.349523125
grams = ounces x 28.349523125
Rounded for the kitchen: 1 oz is about 28 g, 4 oz about 113 g, 8 oz about 227 g and 16 oz (1 lb) about 454 g. NIST's metric kitchen table uses the same rounded figures.
Weight ounces and fluid ounces are different units
An ounce (oz) is a weight. A fluid ounce (fl oz) is a volume, about 29.6 mL in the US. They only line up for water and similar liquids, where 1 US fl oz weighs about 29.6 g against 28.3 g for 1 oz. For anything else, such as honey or flour, a fluid ounce and a weight ounce are far apart. If your recipe says "8 oz" next to a liquid, check whether it means fluid ounces; the ml to fluid ounces converter handles those.
Common conversions
| Grams | Ounces | Pounds |
|---|---|---|
| 1 g | 0.0353 | 0.0022 |
| 5 g | 0.176 | 0.011 |
| 10 g | 0.353 | 0.022 |
| 25 g | 0.882 | 0.0551 |
| 50 g | 1.76 | 0.11 |
| 100 g | 3.53 | 0.22 |
| 125 g | 4.41 | 0.276 |
| 200 g | 7.05 | 0.441 |
| 250 g | 8.82 | 0.551 |
| 454 g | 16 | 1 |
| 500 g | 17.6 | 1.1 |
| 1,000 g | 35.3 | 2.2 |
| Ounces | Grams |
|---|---|
| 0.25 oz | 7.09 |
| 0.5 oz | 14.2 |
| 1 oz | 28.3 |
| 2 oz | 56.7 |
| 3 oz | 85 |
| 4 oz | 113.4 |
| 6 oz | 170.1 |
| 8 oz | 226.8 |
| 12 oz | 340.2 |
| 16 oz | 453.6 |
| 32 oz | 907.2 |
Pounds and ounces
Packaged food in the US is often labelled in pounds and ounces together. The converter shows both when you convert to pounds: 500 g is 1.1 lb, which is 1 lb 1.6 oz. A kilogram is 2.2 lb, or 2 lb 3.3 oz.
Rounding on a kitchen scale
A kitchen scale that reads to 1 g in metric mode often reads to 0.1 oz in imperial mode. A 0.1 oz step is 2.8 g, so the gram setting is nearly three times finer. For small amounts such as yeast, salt or baking powder, weighing in grams gives the better reading.
| Unit | Exact size | Definition | Source |
|---|---|---|---|
| Ounces | 28.349523125 g | 1 avoirdupois ounce = 1/16 pound | NIST Handbook 44 (2019) |
| Pounds | 453.59237 g | 1 avoirdupois pound = 453.59237 grams | NIST Handbook 44 (2019) |
| Grams | 1 g | 1 gram | NIST Handbook 44 (2019) |
| Kilograms | 1000 g | 1 kilogram = 1000 grams | NIST Handbook 44 (2019) |