How Much Metal Roofing Do I Need? Panels, Length and Trim
Part of the project planners: Planning a shed, pergola, garage slab or coop and Planning a roof replacement.
A 40 × 30 ft building with a 4/12 pitch, a 12 inch eave overhang and a 6 inch gable overhang has a slope length of about 17 ft, so it needs 30 panels of 36 inch coverage (14 on each side) in 17 ft lengths, 41 ft of ridge cap, 82 ft of eave trim and 67 ft of rake trim. The metal roofing calculator does your own roof.
Panels for common building sizes
4/12 pitch, 12 inch eave overhang, 6 inch rake overhang, 36 inch coverage, 5% extra:
| Building | Panels | Panel length | Roof (squares) | Ridge cap |
|---|---|---|---|---|
| 24 × 24 ft | 19 | 14 ft | 6.9 | 25 ft |
| 30 × 20 ft | 24 | 12 ft | 7.2 | 31 ft |
| 40 × 30 ft | 30 | 17 ft | 13.8 | 41 ft |
| 50 × 36 ft | 36 | 21 ft | 20.4 | 51 ft |
| 60 × 40 ft | 45 | 23 ft | 27.0 | 61 ft |
How the pitch changes the panels
For the 40 × 30 ft building:
| Pitch | Panel length | Panels | Roof (squares) |
|---|---|---|---|
| 3/12 | 17 ft | 30 | 13.5 |
| 4/12 | 17 ft | 30 | 13.8 |
| 6/12 | 18 ft | 30 | 14.7 |
| 8/12 | 20 ft | 30 | 15.8 |
| 12/12 | 23 ft | 30 | 18.6 |
How to measure
- Measure the length of the building along the ridge, and add the gable overhangs.
- Measure the width, halve it, add the eave overhang, and multiply by the pitch factor to get the slope length.
- Divide the roof length by the coverage width of one panel (not the sheet width) and round up.
- Order panel lengths in whole feet. The last panel on each side is often cut to width.
- Add the trim: ridge cap, eave drip edge, rake trim, and closure strips.
Before you order
- Check the minimum pitch, the underlayment, and the fastener pattern for your panel profile.
- Plan for ice and water shield at the eaves and valleys in cold climates: see the ice and water shield guide.
- Metal roofing is slippery and sharp. Use a harness and the right shoes, and wear gloves.
- Allow for the heat expansion of long panels in the fastener pattern and the trim.
- Check for snow guards if you get snow.
See also the roofing calculator for shingles. Estimates only: check your local code and the panel maker's instructions.
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 with a 4/12 pitch, each 17 ft long, with 5% extra.
How long should the 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, and 20 ft at 8/12.
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 one panel, and add the trim. The roof here is 1,383 ft², or 13.8 squares.
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.
Do coverage widths matter?
Yes: the panel width is what counts, not the sheet width. With 24 inch panels the roof needs 21 on each side instead of 14.
More guides
Tools & materials for this project
As an Amazon Associate we earn from qualifying purchases. These links do not change what you pay.
Estimates only. Quantities depend on your materials, site and supplier. Confirm important numbers before you order, and follow local building codes for anything structural.