Metal Roofing Panels Calculator
Work out how many metal roofing panels you need from the roof area or from the roof length, width and pitch: panels per side, cut lengths or stock lengths with end laps, linear feet, screws or standing-seam clips, ridge, eave and rake trim, closures, underlayment and cost.
How it works
Area mode: coverage per panel = (width ÷ 12) × length · panels = ceil(area × (1 + waste%) ÷ coverage per panel) · Roof mode: slope length = run × √(1 + (rise ÷ 12)²) · panels across = ceil(roof length × 12 ÷ coverage width) · pieces per run = 1 cut panel, or 1 + ceil((slope − stock length) ÷ (stock length − end lap)) · panels = across × sides × pieces per run × (1 + waste%) · linear feet = panels × panel length · screws ≈ 80 per 100 sq ft · clips = panels × (panel length ÷ spacing + 1) · trim = edge length × 1.05 ÷ 10 ft
Metal panels are sold by their coverage width, the net width they add to the roof once the seams or laps interlock, which is narrower than the raw sheet. With only the roof area, the calculator divides the area (grown by a waste factor for cuts at hips, valleys and edges) by the area one panel covers and rounds up. With the roof length, width and pitch it counts the way an installer does: the slope length from eave to ridge sets the panel length, the eave length divided by the coverage width gives the panels across each side, and each run is either one panel cut to length or several stock panels joined with end laps. The same measurements give the trim: ridge cap along the ridge, eave trim along the eaves and rake trim up both gable edges, plus foam closures under the trim, screws or standing-seam clips, and synthetic underlayment.
Worked example
For an 1,800 sq ft roof with 36-inch (3 ft) coverage panels 12 ft long, each panel covers 3 × 12 = 36 sq ft. Adding 10% waste gives 1,980 sq ft, so 1,980 ÷ 36 = 55 panels, totalling 660 linear feet. Measured instead as a 40 × 30 ft gable roof at 4/12, the slope length is 15 × 1.0541 = 15.81 ft, so panels are cut to 15 ft 10 in. Each side takes 480 ÷ 36 = 13.3, so 14 panels: 28 panels exactly, 31 with 10% waste. The trim is 40 ft of ridge cap, 80 ft of eave trim and 63 ft of rake trim.
Sources: Inch Calculator — metal roofing panels from roof size, pitch and exposed width · Omni Calculator — metal roof cost, measured or footprint-and-pitch area
Frequently asked questions
Is coverage width the same as panel width?
No. The raw sheet is wider than what it covers on the roof, because the edges form the seam or overlap with the next panel. Always size from the coverage (net) width — for a 36-inch coverage panel the physical sheet is often about 38–39 inches.
How much waste should I allow for metal roofing?
Measured by roof dimensions, the count is already exact, so 0–5% covers a miscut on a simple gable. By area, allow about 10% for a simple roof and 15% or more for roofs with hips, valleys, dormers or diagonal cuts, because panels have to be trimmed to the angle.
Should I buy cut-to-length or stock-length panels?
Cut-to-length panels run in one piece from eave to ridge, so there are no end laps to seal and less waste. Stock lengths from a store are cheaper to pick up but need 6-in end laps with sealant, and the top piece is trimmed. Switch off cut-to-length to see how many stock panels and laps you need.
How many screws do I need for a metal roof?
For 36-inch exposed-fastener panels over purlins 24 in apart, about 80 screws per 100 sq ft of roof, plus stitch screws on the side laps if the maker calls for them. Closer purlins or high-wind codes need more. Standing seam panels use hidden clips instead, usually every 24 in along each seam.
Should I order extra panels?
Yes — order at least one or two spare full-length panels. Matching the exact color and coating batch later is difficult, and a single miscut can hold up the whole job.
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This calculator is for educational purposes. Double-check important results before acting on them.