avoirdupois weights

   the common traditional system of weights in all the English-speaking countries.

   Until the introduction of the metric system, almost all weights were stated in avoirdupois units, with only precious metals being measured by troy weights and pharmaceuticals by apothecary weights (see above). The name of the system comes from the Old French phrase avoir du pois or aveir de pois, "goods of weight," indicating simply that the goods were being sold by weight rather than by volume or by the piece. The system is based on the avoirdupois pound¹ of 7000 grains. The pound is divided into 16 ounces¹, each divided further into 16 drams¹. The avoirdupois system was introduced in England around 1300, replacing an older commercial system based on a "mercantile pound" (libra mercatoria) of 7200 grains divided into exactly 15 troy ounces². Scholars believe the avoirdupois pound was invented by wool merchants and modeled on a pound of 16 ounces used in Florence, Italy, which was an important buyer of English wool at the time. The avoirdupois weights quickly became the standard weights of trade and commerce. They continue to be used for most items of retail trade in the United States, and they remain in some use in Britain, Canada, and other areas of British heritage despite the introduction of metric units there.