How this calculator works
The ounce used for food and postal weights is the avoirdupois ounce, defined in 1959 as exactly 28.349523125 grams. Sixteen of these ounces make one avoirdupois pound of exactly 453.59237 grams. The ounce on this page is never the troy ounce used for precious metals, which is larger at 31.1034768 grams, and it is never the fluid ounce, which measures volume rather than mass.
Formula
ounces = grams / 28.349523125. grams = ounces x 28.349523125. pounds = grams / 453.59237. kilograms = grams / 1,000. milligrams = grams x 1,000.
Worked example
100 g is 3.52740 oz, 0.220462 lb and 100,000 mg. 1 oz is 28.3495 g. 8 oz is 226.796 g, because 8 x 28.349523125 = 226.796185. 1 lb is 453.592 g or 16 oz.
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Frequently asked questions
Is this the same ounce as a troy ounce?
No. This page uses the avoirdupois ounce of 28.349523125 g. A troy ounce, used for gold, silver and other precious metals, is exactly 31.1034768 g, which is about 9.7 per cent heavier.
Why does an ounce have an exact definition?
The 1959 international yard and pound agreement defined the pound as exactly 0.45359237 kg and the ounce as one sixteenth of it. Before that agreement, different countries used slightly different pounds.
Is a fluid ounce a weight?
No. A fluid ounce measures volume and depends on the density of the liquid. A US fluid ounce is 29.5735 mL and an imperial fluid ounce is 28.4131 mL.