This calculator is based on the "Brzycki Formula" (created by Matt Brzycki). This is a way to way to predict your 1RM max - from reps to failure. This formula is based on noted near linear relationship between the number of reps to failure and the percentage of maximum load. It appears as if the relationship is not quite linear beyond about 10 reps. Therefore, this formula is only valid for predicting a 1RM when the number of reps to failure is less than 10. If the reps exceed about 10, then the test becomes less accurate.

Here are some of examples of the weights I can do. I have yet to do a 1 rep max to see how accurate it is because I don't want to injure myself.
Amounts current as of February 21, 2000.
Squat - 280 lbs. * 10 reps = 373.4 lbs.
Dead Lift - 305 lbs. * 8 reps = 378 lbs.
Bench Press - 230 lbs. * 6 reps = 267.1 lbs.

This equation and other good bodybuilding tips can be read on the Cyberpump web site. In particular, read the FAQ.

Disclaimer: This calculator is only accurate for repitions less than or equal to 10.