The avoirdupois pound is the pound in general use today...This pound is of 7000 grains, and is split into 16 ounces (each, therefore of 437.5 grains). Each ounce is divided into 16 drams...

The Troy pound was of 5760 grains, and was divided into 12 ounces, so a troy pound is lighter than an avoirdupois pound, but a troy ounce (at 480 grains) weighs more than an avoirdupois ounce (EA)

avoirdupois weights:
16 drams = 1 ounce
16 ounces = 1 pound
7 pounds = 1 clove
14 pounds = 1 stone
28 pounds = 1 tod
112 pounds = 1 hundredweight
364 pounds = 1 sack
2240 pounds = 1 ton
2 stones = 1 quarter
4 quarters = 1 hundredweight
20 hundredweight = 1 ton

NB: The sack is not in common use. There was a 'Butchers stone' of 8lb until the end of 1939...

(from http://home.clara.net/brianp/weights.html)