Abstract: A door jamb square made of two extensions, a vertical extension and a horizontal extension. Both extensions are provided with bubble spirit levels and are attached forming a right angle, that can be fit into the corner of a door jamb to square that door jamb. The door jamb square is secured to the door jamb using a nailing plate, web plate and a bolt. The web plate is placed within the webbing of the door jamb square, covered by the nailing plate. The web plate and nailing plate each have an aperture aligned and fitted with the bolt. Additional sheetrock screws are used to secure the other side of the nailing plate and door jamb assembly to the door jamb.