Mass and Weight Conversion Definitions

Ounce Avoir

An avoirdupois ounce is equal to 437.5 grains. The ounce is commonly used as a unit of mass in the United States and around the World.

Ounce Troy

A troy ounce (abbreviation: t oz) is equal to 480 grains. Today, the troy ounce is used only to express the mass of precious metals such as gold, platinum or silver.

Pound Avoir

The pound (abbreviations: lb or, sometimes in the United States, #) is a unit of mass in a number of different systems, including various systems of units of mass that formed part of English units, Imperial units, and United States customary units. Its size can vary from system to system. The most commonly used pound today is the international avoirdupois pound.

Pound Troy

Troy weight originates from what was called the troy system of mass and dates back to before the time of William the Conqueror. The troy pound is no longer in general use. In Canada, Australia, the UK, and other places the troy pound is no longer a legal unit for trade. In the United Kingdom, the use of the troy pound was abolished on 6 January 1879. The troy pound is still used for measurements of precious metals such as gold, silver, and platinum, and sometimes gems such as opals.

Full descriptions are available on Wikipedia.