Chevy Sonic specs

Under 2/32" on the brake pads won't pass inspection in most states. Anything under 4/32", I'd recommend swapping, especially if you have any shimmying when braking. I always replace the rotors when replacing the pads, so no need to measure. If you want to reuse the rotors, use a micrometer, the thickness should be stamped on the rotor. Shoes should be replaced around the same thickness.