Abstract: A gauge is disclosed to grid in the location of sprinkler lines above grid type suspended ceilings. The gauge is used after the grid is installed but before the overhead sprinkler system is completed and before the ceiling tiles are installed. The gauge includes a plurality of arms, preferably three which have lengths approximating 1/2 of the grid opening dimension and are all pivotal and extendable, if necessary to engage the grid system and locate a central body to which the arms are secured. When extended, the arms define the center of the grid opening. An extendable arm is secured to the central body and may be manually extended upward to locate the center of the grid opening at the structural support for the sprinkler distribution system. A drop branch line from the distribution system at the location identified by the gauge is installed and a sprinkler head attached to the drop branch line.