Hello I have a question about the box squat. Would you use the same max for box squat from a regular squat or is there a percentage that gets taken off from a regular squat?
Why do you need to know your box squat max? Just max on it if you need to be precise. If DE work, then just base it off your squat max like any other DE work.
This would be a huge mistake because they're different exercises with different ranges of motion, different muscle recruitment, and different leverages.
There's no set ratio because there are (unfortunately) different depths of back squats and different heights of box squats, not to mention different lengths of pause time on the box. This thread in the Powerlifting forum from last year had a bunch of guys discussing it, actually.