Metal Roofing Calculator: Panels, Lengths & Screws
Panels and their cut length for your roof from its size, pitch and the panel’s coverage width, with screws and trim.
By Marko VisicBSc Physics, University of Ljubljana
28panels
36″ panels, each 18 ft 1 in long
15.03 squares of roof, 506 ft of panel
- Roof area
- 1,503 sq ft
- Panel length
- 18 ft 1 in
- Panels per side
- 14
- Panel run
- 506 ft
- Screws
- about 1,203
- Squares of roof
- 15.03
- Eave trim
- 84 ft
- Rake (gable) trim
- 72 ft
- Ridge cap
- 42 ft
Screws at Fabral’s 80 per square of steel panels; McElroy notes no single fastener rule fits every panel, so use your panel’s schedule. Fabral lets panels run 1 to 2 inches past the eave. The least pitch for every roofing, metal included, is in the roof pitch guide.
28 panels, each 18 ft 1 in long, about 1,203 screws
Metal panels run from the eave to the ridge, so count them across each eave. A 40 by 30 ft gable with 1 ft overhangs at 6/12 takes 28 panels of 36-inch coverage, each 18 ft 1 in long, 14 per side, held by about 1,203 screws at Fabral’s 80 per square.
The panel’s coverage width decides the count and the slope decides the length, so the same roof takes fewer, wider exposed-fastener panels than standing seam.
How to calculate metal roofing panels
Count across, then measure up. The number of panels on a plane is its eave length divided by the panel’s coverage width, rounded up; the length of each panel is the slope from the eave to the ridge plus the bit that hangs past the eave.
Panels per side = (length + 2 × overhang) ÷ coverage width, rounded up
Panel length = half the width with overhangs × √(1 + (pitch ÷ 12)²) + overhang past the eave
Screws = roof area ÷ 100 × screws per square
Example: the eave is 42 ft, so 36-inch panels take 14 per side. The run from the eave to the ridge is 16 ft; at 6/12 that is 17.89 ft along the slope, and with 2 inches past the eave the panels are cut at 18 ft 1 in. The roof is 1,502.6 sq ft, so about 1,203 screws at 80 per square.
How to measure a roof for metal roofing
Measure the walls and the overhangs from the ground, and find the pitch with the roof pitch calculator. For the panel length, the run is half the building’s width including the overhangs on a gable, the whole width on a shed. Panels hang past the eave: Fabral allows 1 to 2 inches.
Long runs may need two panels lapped end to end. Metal Sales recommends its Classic Rib from 5′ up to 45′ long, and Fabral laps panel ends 12″.
Panel coverage widths
Coverage width is what one panel covers once its rib laps the next one, narrower than the sheet itself. McElroy puts it plainly: exposed-fastener panels most often cover 36″, standing seam 16 to 18″.
For lapped panels the 2021 IRC sets 3/12 as the least slope without lap sealant and ½/12 with it; standing-seam systems may go to ¼/12. The roof pitch guide lists the minimum for every roofing.
Screws for metal roofing
Exposed-fastener panels are screwed through the face into the deck or purlins. Fabral specifies 80 galvanized screws per square of its steel panels, with stainless screws for aluminum. McElroy notes no single rule covers every panel and maker: each system is tested with its own pattern, so the schedule for your panel wins. The calculator uses Fabral’s count as an estimate; standing seam is held by concealed clips instead.
Trim: eaves, rakes, ridge and hips
Trim is sold by length to cover the roof’s edges: eave trim along the eaves, rake or gable trim up the sloped ends, and cap along the ridge and the hips. Rakes and hips follow the slope, so they are longer than their plan length.
| Roof shape | Panels | Eave trim | Rake trim | Ridge and hip cap |
|---|---|---|---|---|
| Gable | 28 | 84 ft | 72 ft | 42 ft |
| Hip | 50 | 148 ft | 0 ft | 106 ft |
| Shed | 14 | 42 ft | 72 ft | 0 ft |
Metal roofing calculator FAQ
How many metal roof panels do I need?
Divide each roof plane’s eave length by the panel’s coverage width and round up. A 42-foot eave takes 14 panels of a 36″ rib panel, so a gable with two such sides takes 28.
How long should metal roof panels be?
As long as the slope from the eave to the ridge, plus the overhang past the eave. Fabral allows 1 to 2 inches. On a 6/12 roof with a 16-foot run, that is 18 ft 1 in.
How many screws per square of metal roofing?
Fabral specifies 80 galvanized screws per square of its steel exposed-fastener panels, a square being 100 square feet. Other makers publish their own schedules; McElroy notes there is no single fastener rule for every panel.
How do you measure a hip roof for metal?
Measure the four eaves, the overhang and the pitch. Each plane takes its eave length divided by the coverage width in panels, cut at the hips, so the pieces near the corners are short and the longest runs up the middle of each plane. The calculator counts the pieces and gives the longest.
Sources & method
Panels per plane are the eave length divided by the coverage width, rounded up; panel length is the run times √(1 + (pitch ÷ 12)²) plus the overhang past the eave, rounded up to the inch. Screws are the roof area in squares times 80, Fabral’s figure for its steel panels. Trim lengths are the eaves, the rakes and hips along the slope, and the ridge. Coverage widths and limits are from Metal Sales, Briggs Steel and McElroy; slope minimums from the 2021 IRC.
- Metal Sales Manufacturing Corporation. Classic Rib Condensed Technical Reference. MSMC/1-2026
- Briggs Steel. 5V Crimp Panel technical sheet. Rev 07/19
- McElroy Metal. 8 FAQs for Installing Exposed Fastener Metal Roofs. Jul 31, 2025
- Fabral. Storage and Installation Instructions: Metal Roofing and Siding, Aluminum and Galvanized Steel. 98-32-002 (11/13)
- International Code Council. 2021 IRC Chapter 9 Roof Assemblies, Section R905 Requirements for Roof Coverings. 2021 IRC
- Owens Corning. DIY Roofing: Re-Roofing Tips (What is a “Roofing Square”?). page read Nov 14, 2026
- Roof Square Footage Calculator: Area & Roofing SquaresRoof surface and roofing squares from the footprint, overhang and pitch.
- Roof Pitch: What It Means & the Minimum for Each RoofingThe lowest pitch the 2021 IRC allows for every roofing, metal panels included.
- Shingle Calculator: Bundles, Starter & Ridge CapBundles, starter strip and ridge cap for a shingle roof of the same size.