One of the parts that you must replace in a car with lots of use is the brake rotors. The rotors are the part that the actual brake pad compresses onto in order to stop the vehicle. When the brake rotors are pitted or have grooves in them, you will need to replace them for consistent braking. Finding what proper size rotors to use is something you should need to know when you replace them.
Sizes Stamped on Rotor
If the rotor has not been worn down too much, you will be able to see the size stamped right on the rotor itself. It will be in millimeters and usually on the wheel side of the rotor.
Measure Diameter of Used Rotor
Another way to get a good idea of the size of rotor you will need for your vehicle is to measure the diameter of the used rotor. This will give you a fairly accurate reading.