16 Avoirdupois oz = 1 Avoirdupois lb (our measures in the grocery store and on the scale in the bathroom)

12 troy oz = 1 troy lb (used in precious metals)

1 Avoirdupois lb = 7,000 grains (I use grains in reloading, powder and bullet weight)

1 troy lb = 5,760 grains

1 troy ounce = 480 grains

1 Avoirdupois lb = 7,000/480 = 14.583 troy ounces

http://en.wikipedia.org/wiki/Troy_weight

If you want metric, 1 troy ounce = 31.103 grams

pennyweights are included in the link above.

100 kg = 220 Avoirdupois lb = 3,215.1 troy ounces