Overview

The avoirdupois system is a system for measuring mass and weight that centers on the pound composed of 16 avoirdupois ounces. The standard avoirdupois pound is defined as 7,000 grains and exactly 453.59237 grams. In everyday language this system is commonly used to state body weight, grocery weights, and shipping weights in the United States and to a lesser degree in Canada, the United Kingdom, and Ireland. The word "avoirdupois" reflects historical trade usage and distinguishes this set of units from other systems such as troy or apothecaries' weight.

Units and conversions

The system arranges larger and smaller units around the pound. Key units and relations include:

  • Pound: 1 pound = 16 ounces = 7,000 grains = 453.59237 grams.
  • Ounce: 1 ounce = 1/16 of a pound ≈ 28.349523125 grams.
  • Grain: the smallest common unit, 7,000 grains = 1 pound.

History and development

Originating in medieval Europe, the avoirdupois system developed as a practical set of weights for general commerce, especially for goods traded by weight such as wool and dry commodities. The term entered English from Anglo-Norman and Old French usage. Over centuries the definitions were refined and eventually tied to standardized measures that could be converted to metric values. Legal adoption and international agreements in the 19th and 20th centuries fixed exact metric equivalents.

Modern use and distinctions

Today, the avoirdupois system is integral to the United States customary units and remains in colloquial use in Canada (Canada), the United Kingdom (UK) and Ireland (Ireland) for many everyday contexts. It is distinct from the troy system (used for precious metals) and the apothecaries' system (historical medical dosing), which use different relations between pounds, ounces and grains. For authoritative references on the pound and ounce see general overviews of the United States customary and international practices.

Practical examples

Typical applications include stating body weight in pounds and ounces, expressing the weight of packaged food items, and calculating freight and postal charges. When precision is required, especially in scientific or international contexts, weights are converted and reported in metric units (kilograms and grams) alongside avoirdupois values.