Troy System of Units -- from Eric Weisstein's World of Physics

Units and Dimensional Analysis

Units

Systems of Units

Troy System of Units

A system of mass units use to measure precious metals (c.f. avoirdupois system of units). While there are 16 avoirdupois ounces in one avoirdupois pound-mass, there are only 12 troy ounces in one troy pound. However, the troy and avoirdupois units of grain are equal. The system is summarized in the following table.

unit	abbrev.	value	metric
troy pound	lb t	12 oz t	373 g
troy ounce	oz t	20 pwt	31.103 g
pennyweight	pwt	24 gr	1.555 g
grain	gr	1/24 pwt	0.0648 g

Avoirdupois System of Units

Woolf, H. B. (Ed. in Chief). Webster's New Collegiate Dictionary. Springfield, MA: Merriam, p. 1329, 1980.