Grams to Milligrams

About Grams and Milligrams

Grams (g): Originally defined in 1795 as the mass of one cubic centimeter of water at 4°C; now defined as one thousandth of a kilogram, with the kilogram defined since 2019 by the Planck constant. Common uses: Cooking (especially baking), nutrition labels, postal weight for small parcels, jewelry, and almost any precise mass measurement outside the United States.

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 gram and milligram.

The exact relationship is milligrams = grams × 1.00000000e+3, 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 grams 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.