Here is a helpful and seemingly proven easy "guide" for disk thicknesses:
If your brake light is on and you have a lip whose thickness is no more than that a "Dime" - I might used them again.
"Pennys" - its about time to change them
"Nickel" - Regardless brake light or no hurry up and change em'
Here are the official thicknesses of the US coins:
Penny 1.57 mm
Nickel 1.98 mm
Dime 1.35 mm
Source: Penny Dime Nickel
For pads I am totally tired of brake dust. I have been using PBR Delux pads. Work very well and almost no brake dust.