Metal roofing calculator

How metal roof panels are calculated

Metal panels run from the eave to the ridge, so you need two numbers: how long each panel is and how many fit side by side along the eave. Both come from the same footprint and pitch as the roof area calculator.

On a hip roof every side has an eave, so both L′ and W′ use the eave overhang. Panels are counted per side for gable and shed roofs, and by area for hip roofs, where the triangular ends are cut from full panels:

A porch or wing at a different pitch goes in as its own section. Each section gets its own panel length and panel count, rounded up separately, because panels of different lengths can't be shared. Screws, trim, closures and underlayment are worked out once on the combined lengths and area.

The accessories follow from the roof area and edge lengths:

Worked example: 40 × 30 ft gable roof

The calculator opens on a 40 × 30 ft gable roof at 6/12 with 12 in eave and rake overhangs, 36 in coverage panels and 5% extra.

1. Slope factor: √(1 + (6 ÷ 12)²) = 1.118.
2. Footprint with overhangs: 42' × 32' = 1,344 ft², so the roof area is 1,344 × 1.118 = 1,503 ft², or 15.03 squares.
3. Panel length: 16 ft run × 1.118 = 17.89 ft, ordered at 18 ft.
4. Panels per side: 504 in ÷ 36 in = 14. Two sides make 28, and 28 × 1.05 = 29.4, so order 30 panels (536.7 ft of panel in total).
5. Screws: 1,502.6 ft² ÷ 100 × 80 = 1,202.1, rounded up to 1,203.
6. Ridge cap: 42.0 ft ÷ 10 = 5 pieces. Eave trim: 84.0 ft gives 9 pieces. Rake trim: 2 × 32 × 1.118 = 71.6 ft gives 8 pieces.
7. Closures: 84.0 ft at the eaves and 84.0 ft at the ridge. Underlayment: 2 rolls.

Measuring and ordering tips

• Measure the building along the walls and the overhangs horizontally from the wall face to the fascia, at one eave and one gable end. The calculator adds the overhangs for you.
• Check the pitch with a level and tape: measure the rise over 12 in of run on a rafter tail or the roof surface.
• Panels usually stop about 1 in short of the ridge and run slightly past the eave trim. Those small adjustments normally fit inside the round-up to whole feet, but if the slope length lands just under a whole foot, add a foot.
• Coverage width is the width each panel covers after the side lap, not its full sheet width. Use the number on the manufacturer's profile sheet.
• Panels longer than about 40 ft need a splice or a special order and can be hard to ship and handle. Ask the supplier before you settle on full-length panels.
• For a porch, garage or wing at a different pitch, add it with “+ Add another section” and set its type and pitch. For dormers and valleys, have the supplier draw a panel layout.

Exposed fastener or standing seam

Exposed-fastener panels (classic rib, R-panel, 5V) are screwed through the face into purlins or deck. They are the cheaper choice for barns, sheds and many houses, but most need 3/12 or steeper, and the screw washers need periodic checking. Standing seam panels (usually 12 in to 16 in wide) are held by hidden clips and allow for thermal movement. Low-slope versions with sealed seams can go down to about 1/2:12, so the manufacturer's stated minimum for the exact profile governs. On steep or high roofs, or when you are switching from shingles, a metal roofing contractor can confirm the deck, underlayment and fastening pattern for your wind zone.