How do I know when to increase the amount of weight I lift?

[taichand]

I am trying to find out just when to increae the amount of weight I lift in a given routiine. For instance, if I am performing bench presses, if I start off at 135 (two forty-five plates)@twelve reps, how should my increase in weight correlate to my decrease in reps? In addition, as I continue working out in the future what type of scale should I be using in order to gauge my improvement in strength?

[joshman]

Try increasing the weight to the heaviest you can handle each workout. And by 'handle' I mean completion of all reps with the desired speed.

To gauge, you should keep getting stronger each week.
Examples:
- more total reps, before hitting that rep where you can just barely get it up.
- more weight with the same reps.

If you're interested you can find one-rep max calculators out there, but I would be skeptical about the extrapolations made from the higher rep ranges (8+).