mine are under 1/4 and squealing at light pedal pressure. Ive got about 60K on them, but live at the bottom of a decent hill, so I would suspect possibly needing replacement. I havent torn them apart to look, just looked at the pads while rotating tires the other day

 

I have not torn one of these down yet, but do ours have the little metal "Squealers" on them? That might be what you are hearing. If so, it is time to change.

I would guess 1/4" is probably about the thickness the squealers would start.

 

thats what I was thinking too

 

Dodge will change out life time pads at 3 MM.

 

3mm=1/8 inch

 

Shop said my fronts were at 3mm when I had an alignment (75k mi). They were not squealing yet.
Quick easy change out if your rotors aren't warped.
I scuffed the rotors with some 220grit real good like always since they didn't need to be turned and weren't really worn.
Make sure you watch the brake fluid level when squeezing the calipers back in so you don;t overflow the reservior if any fluid has been added.

 

well i put on 120.000 miles and 6 years on my front pads and rotors

 

mileage is relative, it all depends on what you do, where you go, and how you drive.