As most people have said, you can't be sure without a proper weight check. I teach dry suit classes, and I spend a lot of time on this. I think a lot of dry suit divers are really over-weighted, and I have heard some of them giving what I consider to be very bad advice about how much weight is needed. My normal dry suit needs with a single tank, for example, are under 20 pounds. I think most people my size will be using 30 pounds or more.
Your underwear makes a big difference. The one time I wore my fluffiest underwear with a single tank, my weighting needs skyrocketed. I couldn't believe how much lead I had to put on (and I can't remember what I ended up with).
Your body composition makes a big difference. I know some highly skilled and experienced divers who absolutely need much more weight than I would have ever thought they would.
The amount of gas you carry in the suit makes a big difference. If you carry a lot of gas, you will obviously need more. A pound of lead is roughly equal to a pint of gas volume. A lot of people strongly advocate keeping just enough gas in the suit to keep from feeling squeezed, in which case they would need less weight than some others. Some people, in contrast, are very aware that more air in the suit leads to a warmer dive, and in colder water they are willing to deal with the extra weight in order to get the extra air in the suit.