Quick answer: panels per face = eave length ÷ panel coverage width, rounded up; panel length = depth to ridge × slope factor. Two 42 ft faces with 36 in panels need 28 panels.
How to calculate metal roofing
- Measure each face: length along the eave, and the level depth from eave to ridge including overhang.
- Panels = eave length ÷ coverage width, rounded up.
- Panel length = depth × √(1 + (pitch ÷ 12)²).
Example: a 6/12 gable roof
Two faces, 42 ft along the eave and 16 ft deep, 36 in coverage: 42 ÷ 3 = 14 panels per face, 28 panels. Length 16 × 1.1180 = 17.89 ft, about 17 ft 10⅝ in; 500.9 ft of panel in all.
Coverage width, overlaps at the ridge and eave, and minimum slope are set by the panel maker; the calculator does not check any building code.
Frequently asked questions
How do I calculate metal roofing panels?
For each roof face, divide the length along the eave by the panel’s coverage width and round up. Each panel runs from eave to ridge, so its length is the level depth of the face times the slope factor.
What is the coverage width of a metal panel?
The width each panel adds once it overlaps its neighbour, which is less than its full width. Many exposed-fastener panels cover 36 in (914 mm); standing seam panels are often 12 to 18 in. Use the figure from your supplier.
How long should the panels be?
Depth from eave to ridge (on plan, including overhang) × slope factor. At 6/12 the factor is 1.118, so a 16 ft deep face needs panels about 17 ft 10⅝ in long. Check the overhang and ridge detail your panel needs before ordering.
Does this include screws and trim?
It lists the eave length for eave trim. Fastener counts, ridge and rake trim details depend on the panel system; follow the manufacturer’s layout.
Can I use it for a hip roof?
Only roughly: on hip faces the panels get shorter towards the hips and need cutting. Enter each face as a rectangle and expect more waste.
Is this metal roofing calculator free to use online?
Yes. The CalcWall Metal Roofing Calculator is completely free and works online in any browser, on a phone, tablet or computer. There is nothing to download and no account to create, and the math runs right in your browser, so results appear as you type.