Yesterday I did 635# for my 4th and last set of 10 on the hack squat machine (facing in), and all sets were full ass-to-ground squats. Is there a rough estimate or some formula to estimate what that would be on the back squat?

I am estimating the weight at 635# with 12x45# plates, 2x25# plates, and am just guessing the weight of the empty device to be 45#. I have a hand injury right now so I can’t grasp a barbell to do normal squats, but would like to see where about my regular squat should be. Thanks