Abstract: The present fiberglass panel cutter includes a blade extractor tab for slightly displacing or deflecting scrap pieces of ductboard from their corresponding grooves, a blade height adjuster for controlling the depth of the groove, a blade with aligned apertures for ready removal from a blade mount, a canted handle, and a set of linear channels formed in a lower surface of the cutter for guiding the cutter in a straight line across the ductboard. The present invention further includes a knife with a blade set at a downward angle relative its handle to efficiently make cuts at an arm's length in ductboard which may measure four feet by eight feet. The present invention further includes a square that is infinitely adjustable and convertible between right and left handed orientations.