How do I know when to replace brake pads?

Hello, my front brake pads are down to 6mm. I was told that I don't have to worry until they get below 4mm. What is the original thickness, when buying a car from the factory? Also, any recommendations on what type to get when dealing with a dealership?
Thanks, Barrie
2004 Sunfire, 2.2 (I think, sorry!)

I've never really bothered with the thickness but pay attention to how they feel and any wierd noises. Most pads have wear guides so when they get so far they'll squeal something awfull when you DON'T have the brakes on.

Welcome to AF!! I agree with ponchonutty, go with feel. If your pedal is mushy or you don't have the stopping power you had before change them. Personally I check thickness. If I find they are close to the wear indicators then I change the pads. Not hard to change and if you are slightly mechanically inclined you can do it yourself. Just pick up a manual from the parts store. Also, Don't have the work done by a dealer, they will rip you off on parts and labor. Any mechanic can do the job and probably for a whole lot less. If you put new pads on have the rotors turned to refresh the surface or replace them with new rotors. It is a far better brake job than just replacing the pads. If you go with aftermaket pads use premium pads like Raybestos pads, Performance Friction Carbon Metallics or some other premium pad. The cheap pads don't hold up as well.

that reminds me, the brakes on the van need bled LOL