Abstract: A device and method for determining compliance with building construction codes comprises a block of material with a plurality of planar measuring surfaces separated by appropriate distances that are representative of a maximum or minimum gap space between a door and an adjacent structure, as permitted by industry standards. The appropriate measuring surfaces are inserted in the gap opening between the door and adjacent structure to be tested and quickly and easily indicate whether the gap meets building construction codes. The device functions as one tool to quickly check compliance of all gap openings related to door installations without hindrance from door installation hardware.