For my bench I know my max is right around 275lb. So lets use that as an example.

My 5 rep max is right around 240lb currently (~87% of my max)
Obivously I wouldn't be able to a 5x5 of 240lb or even a 3x5 so I would have to use that figure to get my starting point of a 3x5 or 5x5. I would guess that good starting point for me would be like 205lb (~75% of my max) for a 5x5 and maybe 215lb (almost 80% of my max) for a 3x5... you have to have room to add weight after you start.

For warmups I would do something like:

Use the bar to stretch out for maybe 10 reps then...

115lb x 5 (~40% of my max)
135lb x 5 (~50% of my max)
165lb x 3 (~60% of my max)

Then I might hit 1 acclimation set

185lb x 1 or 2 (~67% of my max) (I might change this to 195lb x 1 (70%) if I were doing a 3x5 ...but it doesn't matter *that* much.

Then start into your 3x5 or 5x5.

The whole idea is to get the blood flowing in your muscles, get them acclimated to the weight, and get your mind into the "zone" of lifting *without* burning out your muscles. The warm up should not be difficult and the acclimation sets should go up smoothly as well.

So if you know what your max for any lift is (or at least close) you can follow a similar system to determine roughly how to warm up/acclimate.

IW