Metal roofing panels run from the eave to the ridge, so you need the number of panels across the roof and their length. Enter the eave length, the length from eave to ridge and the panel coverage width.
Metal roof formulas
Panels per side = eave length (in) ÷ panel coverage width (in), rounded up Panel length = eave-to-ridge length + any extra overhang Roof area = eave length × eave-to-ridge length × planes; squares = area ÷ 100 Ridge cap = eave length (gable roof)
Worked example: a 40 ft gable roof, 16 ft eave to ridge
- Panels per side at 36 in coverage: 480 ÷ 36 = 13.3, so 14.
- Both sides: 28 panels, each 16 ft long.
- Roof area: 1,280 sq ft = 12.8 squares; ridge cap 40 ft.
Coverage width is not panel width
Panels overlap at the side lap, so the coverage width is less than the full width of the sheet. Fabral’s Grandrib 3 panel, for example, covers 36 in. Always use the coverage figure for your panel. Many suppliers cut panels to length, so measure carefully, and add trim pieces (eave, rake, ridge, valleys) separately.
Questions
How many metal roof panels do I need?
Divide the eave length in inches by the panel’s coverage width, round up, and repeat for each roof plane.
How long should metal roof panels be?
The length from the eave to the ridge along the roof, plus any overhang.
What is a roofing square?
100 sq ft of roof surface.
Sources
- Grandrib 3, Fabral.
Used for: 36 in coverage for the Grandrib 3 panel.