Ounce to Kilogram Converter

An ounce (oz) is a unit of mass in the imperial and US customary systems, equal to 1/16 of a pound or approximately 28.35 grams. The avoirdupois ounce is the most common variant.

The ounce derives from the Roman 'uncia' meaning 'twelfth part', originally 1/12 of a Roman pound. The avoirdupois ounce evolved from medieval English trade weights and was standardized as part of the imperial system. It was internationally defined as exactly 28.349523125 grams in 1959.

Ounces are commonly used in the United States for measuring food portions, postal weights, precious metals, and small consumer products. They're standard for nutrition labels, recipe measurements, jewelry, and in retail for products sold by weight in imperial system countries.

A kilogram (kg) is the base unit of mass in the International System of Units (SI), equal to 1,000 grams. It is defined by the Planck constant and represents the mass of the International Prototype of the Kilogram.

The kilogram was originally defined in 1795 as the mass of one liter of water at 4°C. It was later redefined using a physical prototype - a platinum-iridium cylinder kept in France. In 2019, it was redefined using fundamental physical constants, specifically the Planck constant, making it more precise and universal.

Kilograms are universally used for measuring body weight, food quantities, luggage weight, and in scientific applications. It's the standard unit for mass in most countries worldwide, used in commerce, medicine, sports, and engineering. All other metric mass units are derived from the kilogram.