Ounces to Milligrams

About Ounces and Milligrams

Ounces (oz): From the Latin uncia meaning one-twelfth (originally 1/12 of a Roman pound, now 1/16 of an avoirdupois pound); the modern avoirdupois ounce is exactly 28.349523125 grams. Common uses: US cooking, postal weight for letters and small parcels, food packaging in the US, and (as a slightly different troy ounce, 31.10 g) the standard unit for precious metals worldwide.

Milligrams (mg): One thousandth of a gram, used since the metric system was formalized in France in 1799. Common uses: Pharmaceutical dosing (drug tablets, vitamins, supplements), nutrition labels for small quantities, and chemistry.

How the conversion works

Mass conversions use the SI definition: 1 pound is exactly 0.45359237 kilograms. The factor above is the exact ratio between ounce and milligram.

The exact relationship is milligrams = ounces × 2.83495231e+4, which the calculator at the top of this page applies in both directions. Type into either field and the other updates immediately.

When this conversion matters

Converting between ounces and milligrams comes up wherever weight & mass measurements move between systems — from one country's conventions to another's, from a scientific reference to a practical specification, or from one industry's working unit to another's. The calculator and reference table above cover the everyday range; for unusual values you can type any number into either field.