We use Advantage for fleas for all of our dogs and cats. This is the best dosage chart I have ever seen.
http://www.lisaviolet.com/cathouse/advantage.html
Quick list for Advantage, for both cats and dogs:
Cats up to 9 pounds - 0.4ml
Cats 10+ pounds - 0.8ml
Dogs 11-20 pounds - 1.0ml
Dogs 21-55 pounds - 2.5ml
Dogs 55+ pounds - 4.0ml
To further break down the Advantage dosage by weight alone:
0.4ml = 0-10#
0.8ml = 11-20#
1.2ml = 21-30#
1.6ml = 31-40#
2.0ml = 41-50#
2.4ml = 51-60#
2.8ml = 61-70#
3.2ml = 71-80#
If you're using Frontline, use the following guidelines:
Cats 0.5ml
Dogs 11-22 pounds - 0.67ml
Dogs 23-44 pounds - 1.34ml
Dogs 45-88 pounds - 2.68ml
Dogs 89-132 pounds - 4.0ml