Cock size need to experience sensation of Deep Throat?

Serious question for both gals and guys.

On average, how long does an average girth cock need to be before a guy can actually feel the "pop" as the woman pushes his cock from the back of her mouth down into her throat?

Ive never experienced DT before but intend to next week. It will be CBJ for me, probably a few of them in an hour. I hope Im long enough.