This isn't a question about what squat depth is, however, so we're on the same page I am using the IPF's official powerlifting definition:
[...] the lifter must bend the knees and lower the body until the top surface of the legs at the hip joint is lower than the top of the knees.
Whenever I ask a friend about my depth they say I'm going ATG. However, from my perspective, it looks like I'm just hitting parallel. I've started pulling up a bit but I don't want to stop the lift too high now. It is rather difficult to see your hip joint in standard gym shorts.
Usually, I've squatted until I get this feeling like my hip is tilting? My thighs aren't sitting on my heels though which is what I imagine an ATG squat should be.
My question is: does anyone have a good method of how to determine you've reached IPF's squat depth during the squat set?