Your new European cookbook lists 200 grams of flour, but your American measuring cup set only marks ounces. Close enough is not good enough in baking, where a 10 percent error can turn a cake dense. You need the exact gram weight, and you need it without a calculator app open in a flour-dusted kitchen.
This tool converts ounces to grams using the exact international definition of the ounce, so the number you get is the same one a laboratory scale would show.
The formula, and why it is exact
Formula: grams = ounces x 28.349523125
The figure 28.349523125 looks oddly specific, but it is exact by international agreement: since 1959, one avoirdupois ounce has been defined as precisely 28.349523125 grams. Because the definition is exact, the formula has no rounding hidden inside it. It applies to any weight measured in avoirdupois ounces, which covers cooking, postage, and supplements.
How to use it
- Enter the weight in ounces. Fractions and decimals are accepted.
- The tool multiplies your entry by 28.349523125.
- Read the result in grams, usually rounded to one decimal place for readability.
Worked example, step by step
You need to weigh 10 oz of chocolate for a recipe that uses grams.
- Input: 10 ounces.
- Substitute into the formula: grams = 10 x 28.349523125.
- Multiply: 10 x 28.349523125 = 283.49523125.
- Round to one decimal: 283.5 g.
So you weigh out 283.5 grams on the kitchen scale and the recipe behaves exactly as the author intended.
Practical places this matters
Baking with European or professional recipes is the most common use, since grams are far more precise than cup markings. Supplement labels switch between the two systems constantly: a protein powder scoop marked 1 oz is 28.3 g. International sellers convert parcel weights for customs forms, and pharmacies live in both worlds too: a prescription written as 2 oz of cream becomes 56.7 g at the compounding counter, where getting the conversion right is a safety issue, not just convenience. Students use the factor in chemistry class whenever imperial units sneak into a problem.
Mistakes worth avoiding
The classic error is the troy ounce. Gold, silver, and jewelry use troy ounces, and one troy ounce is 31.1035 grams, noticeably heavier. If you convert a gold bracelet with the kitchen factor, you will undervalue it. A second mistake is rounding the factor to 28 too early in a long calculation, which stacks error. Round only the final answer, never the intermediate steps.
A note on precision
Because the conversion factor is exact, all the uncertainty comes from your scale. A kitchen scale reading to the nearest gram is the real limit, not the math. For the reverse direction, see our ounces to pounds converter, and if your recipe jumps between pounds and metric, the pounds to grams converter and kilograms to grams converter complete the set.