Ounces to Kilograms

About Ounces and Kilograms

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.

Kilograms (kg): The SI base unit of mass; defined since 2019 by the Planck constant, replacing a physical platinum-iridium artifact (Le Grand K) that had served as the definition for 130 years. Common uses: Body weight (everywhere except the US), shipping and freight, food packaging, athletics (Olympic lifts, international powerlifting), and any large-scale industrial measurement.

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 kilogram.

The exact relationship is kilograms = ounces × 0.0283495231, 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 kilograms 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.