Brake shoe thickness is measured in millimeters or inches, with the majority measured in millimeters. The minimum thickness a brake shoe should have will vary by manufacturer. However, between 2 and 3 millimeters is generally considered the minimum allowed thickness. Brake shoe thickness can be measured by removing the wheel and brake drum, and measuring the thickness of the brake shoe through the rivet holes. Safety and stopping ability are reduced as brake shoes wear down, and all braking components should be checked regularly in order to assure they are performing properly. Many automotive repair centers will inspect braking systems free of charge.