ounces

An ounce is a unit of measurement used in English-speaking countries, with several related meanings depending on context. The most common is the avoirdupois ounce, used for everyday mass. One avoirdupois ounce equals 1/16 of an avoirdupois pound, or about 28.3495 grams. In this system, there are 16 ounces in a pound, and about 2.2046 pounds in a kilogram.

A separate form, the troy ounce, is used primarily for precious metals. One troy ounce equals 31.1034768 grams, and there are 12 troy ounces in a troy pound.

A third meaning is the fluid ounce, a unit of volume. In the US customary system, 1 US fluid ounce equals 29.573529 milliliters, whereas in the British Imperial system, 1 imperial fluid ounce equals 28.4130625 milliliters. There are 128 US fluid ounces in a US gallon, and 160 imperial fluid ounces in a UK gallon.

The word ounce derives from the Latin uncia, meaning one-twelfth part, reflecting its historical origin in subdivisions of larger units. Today, ounces are still widely used in cooking, packaging, and trade in the United States and, to a lesser extent, the United Kingdom. For scientific purposes, grams and liters are the preferred SI units, while ounces remain common in everyday life and in certain industries.