Abstract: An I-joist jig for cutting a composite I-joist using a circular saw or the like features a support base and a handle. The support base includes an upper surface having a shoulder disposed along an edge forming a guide and a planar region disposed adjacent to the shoulder. A bottom surface of the support base feature a protrusion that is generally perpendicular to the shoulder. In use, support base is placed on the I-joist such that the I-joist jig spans across the ends of the I-joist and over the central region. The protrusion is aligned against an end of the I-joist thereby aligning the shoulder of the I-joist jig and providing a guiding surface for the circular saw.