Are you going for 1RMs? If that's the case, google "1RM calculators." You'll get a bunch of sites that have one of these; you simply type in the weight you're lifting and the number of reps you're doing with that weight and it will calculate your 1RM.
Of course, your real 1RM will likely be higher because max weight you normally lift is done after a number of sets, so you lift less than you would if you were fresh and rested. However, the value you get is a good starting place.
How many attempts do you get at your 1RM? If you get a few, then just start at the calculated value and move up in weight according to how you feel, just like in a PL contest.
Hope this helped!