Ounces to Grams Calculator

Background.

How many grams are in an ounce? Exactly 28.349523125, with no rounding hidden anywhere. Since 1959, when the United States, the United Kingdom and other Commonwealth countries agreed common definitions, the avoirdupois pound has been fixed at 0.45359237 kg. The ounce is one sixteenth of that pound, so dividing by 16 gives the factor to the last digit.

For everyday use 28.35 is close enough; it overstates by under two thousandths of a percent. Kitchen conversion charts often round much harder, to 28 g or even 25 g per ounce. At 28 g a pound comes out at 448 g instead of 453.5924 g, about 1.2% short; at 25 g it is 400 g, nearly 12% short, which a bread dough or a ganache will notice.

The ounce meant here is the avoirdupois ounce of kitchen scales, postal scales and food labels. It is not the troy ounce used for gold and silver, and it is not the fluid ounce, which measures volume.

What is ounces to grams calculator?

The avoirdupois ounce is the everyday US customary and imperial unit of mass, one sixteenth of a pound, or 437.5 grains. It is the ounce printed beside the gram figure on US food packaging and shown on most kitchen and postal scales. The gram is one thousandth of the SI kilogram. Because the pound is defined as exactly 0.45359237 kg, the ounce is exactly 28.349523125 g, and the conversion is a single multiplication with no measured quantity in it.

How to use this calculator.

1. 01Enter the weight in ounces as shown on the scale, recipe or label, using decimals for fractions: 3½ oz is 3.5.
2. 02If the weight is in pounds and ounces, convert the pounds first: 2 lb 4 oz is 2 × 16 + 4 = 36 oz.
3. 03Read the result in grams, then round to what your scale or form can use; most kitchen scales read to the nearest gram.

The formula.

Grams = ounces × 28.349523125. The factor comes from the 1959 definition of the pound, 0.45359237 kg, divided by 16 ounces and multiplied by 1,000 grams per kilogram: 0.45359237 ÷ 16 × 1,000 = 28.349523125. Both numbers in that derivation are definitions rather than measurements, so the factor is exact and every result is as precise as the ounce figure you type in. Going the other way, one gram is about 0.0353 oz, and one kilogram is about 35.274 oz.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Bureau of Standards (1959). Refinement of Values for the Yard and the Pound — establishes the international avoirdupois pound as exactly 0.45359237 kilograms, from which the ounce (1/16 lb = 28.349523125 g) is derived.
2. [2]National Institute of Standards and Technology (2008). NIST Special Publication 811: Guide for the Use of the International System of Units (SI), Appendix B — Conversion Factors.