Depending on where you go to and how the driver uses the brakes. This also does not account for any wear in the drums (IE: Drums that are worn but still in spec You can loose 1/16 of the wear of the shoes hidden by the drums) And express brakes are a whole another story.

pulled out the tape measure. and yep. 3/16 is a lot of life.

i've gone 100k miles on my brakes and still have half thiickness. course 90 ercent of my driving is freeway. and truck has excellent jakes for those down hills.

i just replaced my drum brakes on the car. they were nowhere near 3/16 thick

3/16 is just a hair under 1/4. that's some pretty decent thickness