Krusty,
Here is a link to a website that has a worksheet to estimate how much weight you need. Sounds as if you have dove in the past? If so do you remember how much weight you carried??? How much you weighed at that time??? Compare that to now and that is a starting point.
So many factors play into how much weight...your body weight/body composition (fat vs muscle), what type of suit you are wearing, wet vs dry, neop. vs trilam, your undergarments, what type of tank, aluminum or steel...how efficient you are at your breathing underwater. So we need more information to help you... But what I would recommend is you get a rough estimate...carry several different weights of different mass, like 2, 3, 5 lbs. And try it out...up till recently I always did a weight check from the surface at the beginning/end of a dive to see my weighting...I have learned differently now..it also depends on the pressure in your tank...a very amazing diver took me down after our dive we purged the air out of my tank at about 10 feet, down to 500psi..that is how we did it, I find it to be a more efficient way to be honest with you.
My opinion is this...some may disagree with it...do one of two things..get geared up with 500psi in a tank see if you can stay at 10feet. Or go to a dive after using that website link, add a little extra weight, 6lbs tops..do a weight check before the dive and make any neccasary changes..then dive and return to your 3 minute safety stop at 1000, purge to 500 and check your weight then.
That link is pretty in depth, one time I found a link online ot a calculator of a person's weight to how much lead one needed...can't find it..
However ask a Diving Instructor, they would know best...Please remember to bring an experienced diver with you when testing out your weight.
Hope this helps, Annette
http://dive.scubadiving.com/html/200105buoyancycalc_chart.html