How many pennywieghts in an ounce?

Answer 1

1 Troy Ounce = 20 pennyweights = 480 grains.

A grain is exactly 64.79891 mg; hence one troy ounce is exactly 31.1034768 g, about 10 percent more than the avoirdupois ounce, which is exactly 28.349523125 g. The troy ounce is the only ounce used in the pricing of precious metals, gold, platinum, and silver. The grain, which is identical in both the troy and avoirdupois systems, is used to measure arrow and arrowhead weights in Archery and bullets and powder weights in ballistics.