It's more complicated than a simple formula. If we're talking about olympic lifts (squats, deadlifts, clean & press), start with the bar and increase 5 lbs every day until you start hitting a limit.
Check out Mark Rippetoe's "Starting Strength" [1] for more info. Great program for anyone new to weightlifting.
Check out Mark Rippetoe's "Starting Strength" [1] for more info. Great program for anyone new to weightlifting.
[1] http://startingstrength.com/