Metal Roof Panel Calculator

Metal roofing goes on as long vertical panels that run from the eave up to the ridge, each covering a fixed exposed width. So the panel count is really a question about the eaves, not the whole roof: how many panel widths fit across the bottom edge of each roof plane, and how long does each panel need to be to reach the ridge.

For a simple gable roof there are two planes. The number of panels across one plane is the eave length divided by the panel's exposed width — commonly `36` inches, though `24` and other widths exist. Double that for the two planes. Each panel is cut to the slope length, which is the half-span (half the building width) multiplied by the slope factor for your pitch. A `4/12` roof over a `30`-foot-wide building gives a half-span of `15` feet and a slope length of about `15.8` feet per panel.

From there the trim and fasteners follow. Ridge cap runs the full eave length along the peak. Eave and rake trim run the perimeter edges. Exposed-fastener panels take roughly `80` screws per square — that figure already includes the field screws, the side-lap stitch screws, and the trim screws. The calculator adds your waste allowance to the panel count for off-cuts at hips, valleys, and end walls, then rounds up, because panels and trim are bought whole.

This tool assumes a straightforward gable. Hips, valleys, dormers, and porches change the geometry, so treat the result as a solid starting order and confirm with a panel supplier's takeoff for a complex roof.