Metal roofing calculator: how many metal roof panels and screws do I need?
28 panels
14 across each of 2 roof sides at 36 in coverage, 16 ft long · 12.8 squares · 1,024 screws at 80 per square · for 2 sides of 40 × 16 ft at 4/12
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3/8 or 10' 6".
28 panels
14 across each of 2 roof sides at 36 in coverage, 16 ft long · 12.8 squares · 1,024 screws at 80 per square
Source: Fabral Grandrib 3 product specification 98-32-202L, McElroy R-Panel and Metal Sales PBR-Panel data, and IRC 2021 R905.10.2, read October 23, 2026. Data sheet (PDF)
A roof with 40 ft eaves and two 16 ft sides takes 28 panels of 36 inch coverage, 14 per side, and 1,024 screws at the 80 per square of Fabral Grandrib 3.
A worked example
Two sides 53 ft long and 21 1/2 ft from eave to ridge, at 2 1/2/12, with panels no longer than 12 ft needs 72 panels. 53 ft of eave is 17.67 widths of 36 inches, so 18 runs per side; each 21 1/2 ft run takes two pieces lapped 6 inches. 22.8 squares at 80 screws is 1,824 screws. At 2 1/2/12 the side laps need sealant.
How wide is a metal roof panel?
36 inches of coverage for the common exposed fastener profiles: McElroy R-Panel, Metal Sales PBR and Fabral Grandrib 3 all list 36 inches net. The sheet is wider, but one rib laps the next, so count runs by 36 inches, not by the sheet width.
How many screws per square of metal roofing?
80 screws per square of 100 square feet for Fabral Grandrib 3, by its product specification. A 1,280 square foot roof is 12.8 squares, so 1,024 screws.
What is the minimum pitch for a metal roof?
3/12 for lapped panels without lap sealant, 1/2/12 with sealant and 1/4/12 for standing seam, by IRC 2021 R905.10.2. Some panels ask for more: Fabral recommends 2 1/2/12 and above for Grandrib 3.
What else it is called
Sold as R-panel, PBR panel, AG panel or exposed fastener metal roofing, in custom cut lengths. Searched as a metal roofing calculator, metal roof material calculator or metal roofing screws calculator.
Panels and screws by roof size
| Eave length | 12 ft sides | 16 ft sides | 20 ft sides |
|---|---|---|---|
| 20 ft | 14 panels, 384 screws | 14 panels, 512 screws | 14 panels, 640 screws |
| 30 ft | 20 panels, 576 screws | 20 panels, 768 screws | 20 panels, 960 screws |
| 40 ft | 28 panels, 768 screws | 28 panels, 1,024 screws | 28 panels, 1,280 screws |
| 50 ft | 34 panels, 960 screws | 34 panels, 1,280 screws | 34 panels, 1,600 screws |
| 60 ft | 40 panels, 1,152 screws | 40 panels, 1,536 screws | 40 panels, 1,920 screws |
Two roof sides, each as long as the column heading from eave to ridge. Panels cover 36 in net, as the McElroy R-Panel, Metal Sales PBR-Panel and Fabral Grandrib 3 data sheets give it; screws at the 80 per square of Fabral Grandrib 3. Trim, ridge cap and closures are not counted.
Where the numbers come from
- Coverage and screws: Fabral Grandrib 3 product specification 98-32-202L: «36" Coverage», «80 SCREWS PER SQUARE RECOMMENDED», recommended pitch 2 1/2:12 and above. The McElroy R-Panel lists a «Cover Width 36"» and the Metal Sales PBR-Panel 36 inch coverage for every gauge. Read October 23, 2026. Fabral data sheet (PDF)
- End laps: Metal Sales PBR-Panel installation instructions (4/24): «Lap the highside panel over the eave panel a minimum of 6"». Minimum recommended slope for PBR, 1:12. Read October 23, 2026. Installation manual (PDF)
- Minimum slope: 2021 International Residential Code R905.10.2, read in the 2021 Seattle Residential Code: 3 units in 12 for lapped, nonsoldered-seam metal roofs without lap sealant, 1/2 unit in 12 with applied lap sealant, 1/4 unit in 12 for standing-seam systems. Read October 23, 2026. Read the code chapter (PDF)
- The rest is arithmetic: runs per side = eave length × 12 ÷ 36, rounded up; pieces per run = (side length − 0.5 ft) ÷ (longest panel − 0.5 ft), rounded up; squares = roof area ÷ 100.
The count is panels, not trim: ridge cap, eave and rake trim and closure strips come in their own lengths. The 80 screws per square is the Fabral figure for Grandrib 3; other profiles print their own pattern.
By Javier Miralles · Last updated . How this site is made.
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