I wake up during the night at times, and instead of just going to the head - I have a horrible habit of looking at SB again, so it was 4.30am for me when I posted above. That's why I didn't go into more detail, but then - I also counted on others giving the advice they have here...
We do not yet know if you are speaking of FW or SW diving, nor if you are using an 80 AL tank, a heavier steel one, etc...?
If you are a smaller, more slender person, you will not need nearly as much weight to get down and stay down as an overweight Texan, but these two factors can affect the amount of lead you need by more than 4#.
The way that I like to finally determine how much weight I really need for a dive - then keep in my log book for future reference - is to determine how much I need to get down quickly in case there is a boat coming at me with a nearly empty tank. Of course, this can only be established with a nearly empty tank, completely wet wetsuit & gear, usually at the end of a dive.
After that, all the above posted advise will help a lot...