Metal Roof Calculator
Enter your roof footprint, pitch and panel width. The calculator works out the true sloped area, how many panels to order and how long they need to be, plus screws, ridge cap and eave trim — with an optional cost estimate.
Results
How the metal roof calculator works
Metal roofing is ordered differently from shingles. Shingles are bought by the square and cut on site, so the only number that matters is area. Metal panels are cut to length at the factory and run from eave to ridge in one piece, so you need two numbers: how many panels fit across the eave, and how long each one has to be.
Panel count: eave length ÷ panel coverage width = panels per slope, rounded up, then multiplied by the number of slopes. Panel length: (footprint width ÷ 2) × pitch factor for a gable roof, where the pitch factor is √(rise² + 144) ÷ 12.
Note the words coverage width. A "36-inch" panel is wider than 36 inches overall — the extra is the sidelap that disappears under the next panel. Always calculate on coverage, never on overall width, or you will come up a panel short.
| Profile | Coverage width | Typical use |
|---|---|---|
| Exposed fastener (ribbed / corrugated) | 36" | Barns, shops, budget residential |
| Exposed fastener (narrow rib) | 24" | Residential, tighter rib spacing |
| Standing seam | 16" | Residential premium, concealed clips |
| Standing seam (narrow) | 12" | Architectural, steep visible slopes |
Metal roofing tips
- Metal works at lower slopes than asphalt: most exposed-fastener panels are rated to 3:12, and many standing seam systems go to 1:12 or lower. Asphalt shingles need at least 2:12, which is exactly why metal ends up on low-slope additions and porch roofs.
- Order panels 1–2 inches longer than the slope run so they can overhang the drip edge, then trim at the eave.
- Exposed-fastener panels need roughly 80 screws per square, with neoprene washers. Those washers are the wear item — budget on re-screwing an exposed-fastener roof at around 20 years.
- Standing seam uses concealed clips rather than face screws, which is why it costs more and lasts longer. The clip count is similar; the labor is not.
- Still comparing metal against asphalt? Run the same roof through the roofing calculator and the shingle calculator to price both, and size the gutters while you are up there.
Frequently asked questions
How many metal roofing panels do I need?
Divide the length of your eave by the coverage width of the panel (3 ft for a standard 36-inch panel), round up, then multiply by the number of roof slopes. A 40 ft long gable roof needs 14 panels per slope, so 28 panels in total.
How long do metal roof panels need to be?
The panel has to reach from eave to ridge in one piece, so its length is the slope run: half the building width multiplied by the pitch factor for a gable roof. A 30 ft wide building with a 3:12 pitch needs panels about 15.5 ft long — order 16 ft and trim at the eave.
How many screws per square for a metal roof?
About 80 screws per square (100 sq ft) for exposed-fastener panels, covering both the field screws and the closer spacing at the eave, ridge and side laps. Standing seam roofs use concealed clips instead of face screws.
What is the minimum pitch for a metal roof?
Most exposed-fastener panels are rated down to 3:12, and many standing seam systems are approved to 1:12 or even lower with sealed seams. That is flatter than asphalt shingles, which need at least 2:12 — one of the main reasons metal gets used on low-slope additions and porches.