proper squat? how low? do you go?

[Zaraza]

How low should you go on a proper squad?

 

[AlexTheGreat]

Thighs parallel to the ground.

http://www.exrx.net/Kinesiology/Squats.html

 

[Quagmire911]

Parallel and above=Great stress on the knee.

In a powerlifting squat the hips comes below the knee like Kerpal said, which is probably an inch or so below "parallel".

In olympic squats with the term "ass to grass" is when you go well below parallel. Some do not have the flexibility or bio-mechanics to do this safely however.

So anywhere below parallel, and the important thing is that your back is locked in extension and doesn't round. If you can't go below parallel without your back rounding, you have some flexibility work to be doing, which you should be doing anyway. I have also seen articles by either Mike Roberston or Boyle I believe, stating that muscle imbalances can cause rounding to be a problem as well.