By The Roofing Brief Team. Last reviewed: October 2026.
How many screws per sheet of metal roofing you need is about 28 to 29 on a 3 ft wide, 12 ft exposed-fastener sheet: Western States Metal Roofing’s rule of 80 screws per roofing square (square footage x 0.8) gives 28.8, and its R-panel pattern of 3 panel screws plus 1 lap screw on each 24 in screw line gives 28 across 7 lines. Rake-edge sheets take 5 panel screws plus 1 lap screw per line, or 42 on the same sheet. Metal Sales puts the rule at 80 screws per square for 3 ft wide panels and 40 per square for 2 ft wide panels, and standing seam uses concealed clips instead of exposed field screws.
How many screws per square of metal roofing?
Plan on about 80 screws per square of metal roofing, where one square equals 100 square feet. Western States Metal Roofing gives two equivalent formulas for its 36 in wide 7/8 in corrugated, R-panel/PBR and 7.2 Western Rib panels at 24 in screw lines: square footage x 80%, or squares x 80, so 3,000 sq ft needs about 2,400 screws. The Metal Sales Classic Rib installation guide (effective 8/19) states the same 80 per square for 3 ft wide panels and 40 per square for 2 ft wide panels.
Published counts differ because they count different screws. The 80 per square figure covers field screws on 24 in lines; Western States adds sidelap stitch screws (square footage / 3 / 1.5, or about 667 on 3,000 sq ft) and one lap screw per lineal foot of trim on top. Closer screw lines raise the count: Western States says jobs that are not at 24 in on center usually run 18 in if closer and up to 36 in if further, so 18 in lines add about a third more field screws than 24 in lines.
How many screws per sheet of metal roofing, by panel type?
A 36 in wide exposed-fastener sheet takes 4 to 6 screws per screw line, depending on profile and whether it sits at the rake, per Western States. Multiply by the number of lines on the sheet: at 24 in on center with a line at each end, a 12 ft sheet has 7 lines. Standing seam is the exception: its panels lock over concealed clips, and the clip count is set by the clip spacing in the evaluation report.
| Panel profile | Panel width | Fasteners per panel | Fastening method | Source |
|---|---|---|---|---|
| Corrugated (7/8 in), roof | 37 in typical, sometimes 39 in | 4 per line; 28 on a 12 ft sheet | Exposed, in the high of every third corrugation; no metal-to-metal sidelap screws needed on roofs | Western States |
| R-Panel / PBR, interior sheet | 36 in | 3 panel + 1 lap per line; 28 on a 12 ft sheet | Exposed, in the flat beside each major rib | Western States |
| R-Panel / PBR, rake-edge sheet | 36 in | 5 panel + 1 lap per line; 42 on a 12 ft sheet | Extra panel screws at the end sheets against wind | Western States |
| 7.2 Panel / Western Rib | 36 in | 5 panel + 1 lap per line; 42 on a 12 ft sheet | Exposed, in every panel low; butyl tape at the sidelap | Western States |
| Classic Rib (AG panel), 3 ft and 2 ft | 36 in or 24 in | 80 per square (3 ft) or 40 per square (2 ft) | #10-14 woodscrew; 1/4-14 x 7/8 in stitch screw at the lap | Metal Sales Classic Rib guide |
| Standing seam (Petersen Snap-Clad, Tite-Loc) | 10 to 18 in | Clips at 24 to 60 in on center, 2 screws per clip | Concealed clips, no exposed field screws | ICC-ES ESR-4173 |
The per-line counts assume screw lines 24 in apart with one at each end of the sheet. A longer sheet adds one line, and 4 to 6 screws, for every additional 24 in of length, so a 16 ft interior R-panel carries 36 screws against 28 on a 12 ft sheet.
Screws per sheet chart by panel length
This chart applies Western States’ per-line counts to common sheet lengths at 24 in screw lines, with the 80% rule (36 in coverage x length x 0.8) as a cross-check. Count the rake-edge sheets separately, because they take 6 screws per line instead of 4.
| Sheet length | Screw lines at 24 in | Interior R-panel/PBR (4 per line) | Rake-edge R-panel or 7.2 Western Rib (6 per line) | 7/8 in corrugated roof (4 per line) | 80% rule, 36 in sheet | Source |
|---|---|---|---|---|---|---|
| 8 ft | 5 | 20 | 30 | 20 | 19 | Western States per-line counts |
| 10 ft | 6 | 24 | 36 | 24 | 24 | Western States per-line counts |
| 12 ft | 7 | 28 | 42 | 28 | 29 | Western States per-line counts |
| 14 ft | 8 | 32 | 48 | 32 | 34 | Western States per-line counts |
| 16 ft | 9 | 36 | 54 | 36 | 38 | Western States per-line counts |
| 20 ft | 11 | 44 | 66 | 44 | 48 | Western States per-line counts |
For standing seam, count clips instead: clips per panel = panel length / clip spacing + 1. At the 24 in clip spacing listed for one plywood assembly in ICC-ES ESR-4173 (Petersen standing seam), a 20 ft panel takes 11 clips and 22 clip screws; at 48 in it takes 6 clips and 12 screws.
Coverage width versus actual width, the quantity trap
Order screws off the number of sheets, and count sheets off the coverage width, not the raw sheet width. Western States notes 7/8 in corrugated comes as a 37 in sheet and sometimes as 39 in, and a 39 in sheet still takes 4 screws per line, with one screw moved to the fourth corrugation. Fewer covering inches per sheet means more sheets across the roof, which means more screw lines than the raw sheet dimension implies.
This is the most common reason a screw order comes up short. Divide the eave length by the coverage width on the maker’s cut sheet (36 in for Classic Rib in the Metal Sales guide) to get the true sheet count per course, then apply the per-sheet figure from the chart. A 40 ft eave at 36 in coverage is 13.3, so 14 sheets per course, 2 of them at the rakes.
What screw spacing produces that count?
The count comes straight out of two spacing rules: screw lines run 24 in on center down the panel on solid wood decking (or at every purlin over open framing), and each line takes 4 screws on an interior R-panel or corrugated sheet and 6 on a rake-edge R-panel or 7.2 Western Rib. Lap screws at panel seams run 12 to 18 in on center, per Western States.
On a 12 ft panel that is a line at the eave, five intermediate lines and a line at the ridge, so 7 lines. McElroy Metal’s Multi-Rib / R-Panel installation manual shows 1/4-14 x 7/8 in Lap Tek stitch fasteners at 1 ft 8 in on center. For the exact placement pattern and the rib-versus-flat debate, see our guide on the correct metal roofing screw pattern and our note on where to place metal roofing screws.
How to calculate total screws for your whole roof
To size a full order, convert roof area to squares, apply the 80-per-square rule, add sidelap stitch screws and trim screws by the lineal foot, then add a waste allowance. The steps below follow Western States’ formulas, worked on a 1,600 sq ft R-panel roof.
- Measure total roof area and divide by 100 to get squares. A 1,600 sq ft roof is 16 squares.
- Multiply squares by 80 for field screws: 16 x 80 = 1,280 screws.
- Add sidelap stitch screws for R-panel, PBR or 7.2 Western Rib: 1,600 / 3 / 1.5 = 356 screws (skip this on 7/8 in corrugated roofs).
- Add one lap screw per lineal foot of trim and flashing at eaves, rakes, ridge, hips and valleys. In this example, 180 lineal feet adds 180 screws.
- Add a waste allowance for stripped screws and cut panels; this example uses 10%, then rounds up to full boxes.
| Step | Screws | Formula source |
|---|---|---|
| Field (16 squares x 80) | 1,280 | Western States; Metal Sales |
| Sidelap stitch (1,600 / 3 / 1.5) | 356 | Western States |
| Trim and flashing (180 lin ft x 1) | 180 | Western States |
| Subtotal | 1,816 | Sum |
| Add 10% waste (example allowance) | about 1,998 | Planning input |
If your supplier boxes screws in 250-counts, 1,998 screws is 8 boxes; in 500-counts it is 4. Our metal roofing square calculator can cross-check the panel and screw totals against your exact coverage width.
Add screws at edges, corners, and high-wind zones
Western States already adds screws at the rake-edge sheets (6 per line instead of 4), which it says lessens the likelihood of strong winds ripping the panels off, and engineered fastening schedules go further in the perimeter and corner zones. On a 12 ft sheet that rake-edge rule alone adds 14 screws, 42 versus 28.
ASCE 7, the wind-load standard the International Building Code references, divides a roof into interior, perimeter and corner zones, with the highest uplift at the corners. Panel makers publish fastener spacing by zone in their load tables and product approvals; tightening screw lines from 24 in to 12 in doubles the field count in that zone, from 4 per line every 24 in to 4 per line every 12 in.
| If your roof is | Screw count rule | Source |
|---|---|---|
| 36 in exposed-fastener panel on solid wood deck, normal wind | 80 per square at 24 in lines; 4 per line interior, 6 per line at the rakes | Western States |
| 2 ft wide Classic Rib panel | 40 per square | Metal Sales Classic Rib guide |
| Steel purlins instead of a deck | A screw line at every purlin; count lines from the purlin layout, not 24 in | Western States |
| Screw lines at 18 in on center | About 1.33 x the 24 in count | Arithmetic from Western States’ 24 in basis |
| Perimeter or corner zone, or a coastal or Florida jurisdiction | The maker’s engineered schedule or product approval, not the 80 per square rule | ASCE 7 zones; maker load tables |
| Standing seam | Clips per panel = length / clip spacing + 1, 2 screws per clip | ICC-ES ESR-4173 |
The exact zone width and spacing depend on building height, roof pitch and the local design wind speed. In High-Velocity Hurricane Zone counties such as Miami-Dade and Broward in Florida, the fastener spacing comes from the panel’s product approval.
Trim, lap, and stitch screws people forget
Beyond field screws, a metal roof needs metal-to-metal stitch screws at every sidelap and lap screws at every trim piece: Western States counts one per lineal foot of trim and flashing plus square footage / 3 / 1.5 for sidelaps. These are the fasteners most homeowners leave out of a screw count. Buy them as a separate line on the order.
- Panel sidelaps: stitch screws join panel to panel along the overlapping rib at 12 to 18 in on center per Western States, or 1 ft 8 in in McElroy’s R-panel manual; Metal Sales specifies a 1/4-14 x 7/8 in stitch screw.
- Endlaps: where one panel overlaps another end to end, a screw line at the lap pulls it tight over butyl or mastic tape.
- Trim and flashing: ridge cap, eave trim, rake trim and valley metal take about 1 lap screw per lineal foot in the Western States count.
Field screws for panel-to-wood in the Metal Sales guide are #10-14 woodscrews in 1 in, 1 1/2 in and 2 in lengths (or a plated #10-12 x 1 in pancake-head woodscrew), while stitch screws are the shorter 1/4-14 x 7/8 in metal-to-metal fastener. Order both. For sizing, thread type and coating by substrate, see our guide to the best metal roofing screws. For the full fastening sequence in context, see our metal roof installation guide and the profile-specific notes in our corrugated metal roofing guide.
Frequently asked questions
How many screws per square of metal roofing?
About 80 screws per square, where one square is 100 square feet, for 36 in wide exposed-fastener panels at 24 in screw lines (Western States Metal Roofing; Metal Sales gives the same figure for 3 ft panels and 40 for 2 ft panels). Sidelap stitch screws (square footage / 3 / 1.5) and one screw per lineal foot of trim are added on top.
How many screws per sheet of metal roofing?
About 28 to 29 on a 3 ft x 12 ft exposed-fastener sheet: 4 screws per line on 7 lines at 24 in on center for an interior R-panel or 7/8 in corrugated sheet, or 28.8 by the 80% rule. Rake-edge R-panel sheets and 7.2 Western Rib take 6 per line, or 42 per 12 ft sheet. Standing seam uses clips instead.
How far apart should metal roofing screws be?
Screw lines typically run 24 in on center down the panel on a wood deck; Western States says closer jobs usually use 18 in and wider ones up to 36 in, and over steel purlins the line goes at every purlin. Sidelap stitch screws run 12 to 18 in on center. Perimeter and corner zones follow the maker’s engineered schedule.
Do you screw metal roofing on the rib or the flat?
It depends on the panel. Western States places R-panel and PBR screws in the flat beside each major rib, 7.2 Western Rib screws in every panel low, and 7/8 in corrugated roofing screws in the high of every third corrugation. Follow the maker’s installation guide for your exact profile.
Can you use too many screws on a metal roof?
Yes. Extra screws add penetrations and cost, and over-driving any single screw distorts the washer, which then leaks; under-driving leaves a gap. The Metal Sales guide shows the correct seat as the sealing material slightly visible at the edge of the washer, with a deformed washer marked too tight. Drive the specified count to that seat.
What size screws do you use for metal roofing?
The Metal Sales Classic Rib guide lists #10-14 woodscrews in 1 in, 1 1/2 in and 2 in lengths for panel or flashing to a wood substructure, and a 1/4-14 x 7/8 in stitch screw for panel sidelaps and flashing to panel. Thicker decks or battens call for the longer screw.