Use the mass conversion
One avoirdupois ounce equals exactly 28.349523125 grams. Multiply ounces by that factor to get grams. Divide grams by the same factor to get ounces.
Grams = ounces × 28.349523125
Ounces = grams ÷ 28.349523125
Common food-scale conversions
- 1 oz = 28.35 g
- 2 oz = 56.70 g
- 3 oz = 85.05 g
- 4 oz = 113.40 g
- 8 oz = 226.80 g
The displayed decimals are conversions, not extra measuring precision. A scale that changes in one-gram steps cannot suddenly measure hundredths of a gram because its result was converted.
Keep the nutrition basis attached
If a food entry gives calories for 3 oz and your scale shows grams, convert the 3 oz reference to about 85.05 g. Compare your portion with that gram weight before scaling the calories or macros.
When the package already prints a gram amount beside the ounce serving, use the package value. U.S. labels can show rounded metric equivalents, so a label may print 1 oz as 28 g rather than 28.3495 g.
Use the serving size calculator after converting if you also need to scale calories and macros to the amount eaten.
A fluid ounce is not a food-weight ounce
An ounce on a food scale is a unit of mass. A fluid ounce is a unit of volume. One fluid ounce of oil, syrup, milk, and water will not have one universal weight because their densities differ.
If a recipe or label gives fluid ounces, use a volume measure or a conversion supplied for that exact food. Do not enter a fluid-ounce value here and treat the result as grams.
Ounces and fluid ounces are different units
This is the single most common error in this conversion, and it is easy to make because both are called ounces. An ounce is a weight: one avoirdupois ounce is 28.349523125 grams exactly. A fluid ounce is a volume, and converting it to grams requires knowing the density of the substance.
They coincide only for something with the density of water. For oil, honey, syrup or flour they do not, and treating 8 fl oz as 8 oz introduces an error in whichever direction that food differs.
A recipe calling for ounces of a solid ingredient means weight. One calling for fluid ounces of a liquid means volume. If the recipe is ambiguous and the ingredient is a liquid, it is almost always fluid ounces.
US and UK fluid ounces are not the same either
A US fluid ounce is about 29.57 millilitres. A UK, or imperial, fluid ounce is about 28.41. The gap is roughly 1.16 millilitres, about 4%, which is small on a single measure and adds up across a recipe scaled several times.
The pints diverge much further, since a US pint is 16 fluid ounces and an imperial pint is 20. If a recipe crosses between the two systems, convert to millilitres or grams once and work from there rather than converting repeatedly.
What the converter cannot decide
It cannot identify the food, check a database entry, choose a raw or cooked reference, or calculate calories from weight alone. The same weight of two foods can contain very different nutrition.
Read how to convert ounces and grams for food tracking for a complete label workflow and the mistakes that matter most.