oz to kg converter

How to convert ounces

kilograms = ounces × 0.028349523125
grams = ounces × 28.349523125
ounces = grams ÷ 28.349523125

One international avoirdupois ounce is defined as exactly 28.349523125 grams, so every conversion above is exact rather than approximate. A troy ounce, used for gold, silver and other precious metals, is a different unit: it weighs about 31.1035 grams.

Common ounce conversions

Where these units come from

The ounce has its roots in the ancient Roman unit of weight called the uncia, which represented one-twelfth of a Roman pound, or libra. Over the centuries, as trade and commerce grew, various versions of the ounce evolved throughout Europe.

During the Middle Ages, local measurement systems emerged, and the ounce became a standard unit in several systems. This eventually influenced the later development of the Imperial system used in the United Kingdom and its former colonies, including the United States.

In contrast, the kilogram and gram are products of the modern metric system, developed in France during the late 18th century. Seeking a universal and rational measurement system, French scientists in the 1790s defined the kilogram as the mass of one liter of water under specific conditions.

The gram, one-thousandth of a kilogram, provided a convenient smaller unit for everyday measurements. Based on decimal subdivisions, this system rapidly gained acceptance worldwide for its simplicity and consistency. Since 2019 the kilogram has no longer been tied to a physical object at all: it is defined by fixing the value of the Planck constant, so the unit can be reproduced in any properly equipped laboratory.

Today, while the metric system—comprising kilograms and grams—is used almost universally in science, industry, and daily life across most countries, traditional units like the ounce persist in some regions, particularly in the United States, where they continue to be a familiar part of everyday commerce and cultural practice.