Performance Level (PL) is a discrete safety metric defined in ISO 13849-1 that quantifies the ability of a safety-related control system to perform a safety function under foreseeable conditions. Levels range from PLa (lowest) to PLe (highest), each corresponding to a target probability of dangerous failure per hour. PL is determined through risk assessment and verified against the required PL (PLr) derived from the hazard and risk analysis of the application.