How this calculator works
Metal roofing panels run from the eave to the ridge, so each is as long as the slope plus the overhang, rounded up to a whole foot. The number of panels along each side is the length of the roof divided by the coverage width of one panel. The area is the slope length times the length, for both sides.
Worked example: a 40 × 30 ft building with a 4/12 pitch, 12 inch eave overhang and 6 inch gable overhangs has a slope of 17 ft to order, 14 panels of 36 inch coverage on each side, 30 in all with 5% extra, and 1,383 ft² (13.8 squares) of roof. It needs 41 ft of ridge cap, 82 ft of eave trim and 67 ft of rake trim. On an 8/12 roof the panels are 20 ft long, and with 24 inch panels there are 21 on each side.
Panels by roof size (4/12 pitch, 12 in eave and 6 in rake overhang, 36 in coverage, 5% extra)
Gable roofs.
| Building | Panels | Panel length | Area (squares) |
|---|---|---|---|
| 24 × 24 ft | 19 | 14 ft | 6.9 |
| 30 × 20 ft | 24 | 12 ft | 7.2 |
| 40 × 30 ft | 30 | 17 ft | 13.8 |
| 50 × 36 ft | 36 | 21 ft | 20.4 |
| 60 × 40 ft | 45 | 23 ft | 27.0 |
Tips before you buy
- Check the minimum pitch for the panel you chose, and use the maker's underlayment, closures and screws.
- Metal roofing is slippery when wet or frosty, and dangerous to walk on: use a harness and the right shoes.
- Panels expand and contract with heat, so follow the instructions for fastener position and trim.
- Order a few extra feet of ridge cap, and extra panels in case the factory cuts or damage run short.
- Check your local rules for permits and for snow guards in snowy areas.
Tools & materials for this project
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Frequently asked questions
How many metal roofing panels do I need?
30 panels of 36 inch coverage (14 on each side) for a 40 × 30 ft building, each 17 ft long. A different pitch or coverage width changes it.
How long should metal roofing panels be?
The slope length from the eave to the ridge, plus the overhang, rounded up to a whole foot: 17 ft for this roof.
How do I calculate metal roofing?
Work out the slope length and the length of the roof along the ridge, divide the roof length by the coverage width of a panel, and add trim lengths. The roof area here is 1,383 ft².
What is the minimum pitch for metal roofing?
It depends on the profile: exposed-fastener panels usually need 3/12 or more, and standing seam can go down to 1/12 or less. Follow the maker.
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Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.