How light should first warm-up sets be

[BobEwell]

Mark,

It seems everyone starts their warmup progressions(squats and presses) with the bar which is typically 45 lbs and occasionally 35.

This makes sense if your working sets are well over 100lbs, but what if they are in the 70-100 lbs range for squats and less for bench or overheads?

Is there a rule for this as well. For example, the warmup sets should be at no more than 20-25% of the working set amount?

I got a 15 lbs technique bar for this reason, but am not sure where to start(ie for 100 lbs working squat should the warmups be 20-25 lbs, or just start with
35 or 45 bar?

Thank you

[Mark Rippetoe]

For a 100-pound work set, 45 is light enough to start warmups.