When it comes to brake pads, there isn't a specific measurement that universally dictates when they should be replaced. Brake pads come with a certain thickness when new, and their wear can vary based on factors such as driving conditions, driving style, and the type of brake pad material.
As a general guideline, many manufacturers recommend replacing brake pads when they reach a thickness of around 3 to 4 millimeters. However, it's important to consult your vehicle's owner's manual or contact the manufacturer for the specific recommendations for your make and model of car.
Additionally, it's crucial to consider other factors when assessing the condition of your brake pads. If you notice any signs of brake issues, such as squealing noises, reduced braking performance, or vibrations, it's advisable to have them inspected by a qualified mechanic regardless of the pad thickness.
Ultimately, your safety on the road should be the primary concern. If you have any doubts or concerns about the condition of your brake pads, it's best to have them inspected by a professional who can evaluate their wear and determine if replacement is necessary.