A substrate processing system includes a laser triangulation sensor configured to transmit and receive light through a window of an exterior wall of a substrate processing chamber. A controller is configured to: position the laser triangulation sensor such that the laser triangulation sensor transmits light onto a measurement feature arranged between a first surface of a substrate support and a second surface of a gas distribution device, where the second surface faces the first surface; and while the laser triangulation sensor transmits light onto the measurement feature, determine a first distance between the first and second surfaces based on a difference between: a second distance between the laser triangulation sensor and the first surface measured using the laser triangulation sensor; and a third distance between the laser triangulation sensor and the second surface measured using the laser triangulation sensor.