Engraved on the side of your rotor you can find the minimum operational thickness.
To accurately measure against the minimum thickness use a micrometer at the thinnest point on the surface of the rotor where it meets the pads.
If your rotor needs to be cut or has worn passed this thickness, you’ll need new rotors. You may also discover your rotor has Disc Thickness Variation. Which could be part of a larger problem in your brake system.
