How do you measure the thickness of a brake pad?

Lift the car with a jack on one side after lifting the hand brake for safety. Then take the wheel off by unbolting them. Make sure to place your wheel underneath by the jack for safety. Find the brake caliper and try to find the brake pad underneath it. You want to find the same brake pad on the other side of the rotor. Inside brake pad may be worn more than the outside. Make sure they are more than 2 mm thick. If not, the car needs to be serviced immediately. If not serviced soon, depending on the driving condition, the brake system may fail or the rotor may have to be replaced if serviced too late. Replacing rotors can cost you a bit more than resurfacing them. On the other hand, some people prefer to get new rotors every time they get brake serviced. Rotors should last two or three brake changes, depending on each case of course. However it may be, 2 mm is a common rule for safety reason. You can always ask your technician to measure the brakes for you while changing engine oil, rotating tires or whatever the reason may be for the visit. If they tell you that you need new brakes soon, but you feel otherwise, you can always do it yourself or go to another service center for measurement. They probably won't give you a exact number. They may say something like: "You are about there, do you want to do it today?"