Abstract: A cutting guide system for guiding a portable power saw across workpiece comprising a rectangular shaped guide plate. The guide plate includes an upwardly projecting rib member extending longitudinally along the guide plate between opposite front and rear ends for guiding the portable power saw through a straight cutting path. The guide plate further includes two T-shaped channels situated within the rib member adapted to slidably receive a pair of opposing clamping devices. The T-shaped channels extends longitudinally predetermined distance from the front and rear ends of the guide plate so as to permit the pair of opposing clamping devices to move longitudinally along the channel to engage against the opposing edges of the workpiece. Prior to the initial use of the guide plate, it is trimmed to size by a power saw guided by the rib member so as to specifically tailor the guide plate to the power saw with which was used to make the initial cut.