Panel Count Formula
Metal roofing panels come in specific widths. The number of panels depends on the panel's coverage width (net width after overlap) and your roof's total eave-to-ridge length.
Panels = Roof Width ÷ Panel Coverage Width
Panel Length = Eave to Ridge (slope length)
Standing Seam: 16" coverage width
Corrugated: 24" coverage width
R-Panel: 36" coverage width
Step 1: Measure Roof Dimensions
You need two measurements per roof section:
- Eave length: The horizontal width along the bottom edge (determines panel count)
- Slope length: From eave to ridge along the slope (determines panel length)
For the slope length, use: Slope Length = (Building Width ÷ 2) ÷ cos(pitch angle) + overhang
Step 2: Calculate Panel Count
Example: Gable roof, 40' eave length, standing seam panels (16" coverage):
Panels per side = 40' × 12" ÷ 16" = 30 panels per side × 2 sides = 60 panels total
Step 3: Screws & Fasteners
- Standing seam: Hidden clips, ~2 clips per linear foot of panel. No exposed screws on field panels.
- Corrugated/R-Panel: ~80 screws per roofing square (100 sq ft). Use hex-head self-tapping screws with EPDM washers.
- Ridge cap screws: 2 screws per linear foot of ridge cap.
Step 4: Ridge Cap & Trim
- Ridge cap: Total ridge length ÷ 10' pieces. Add 10% for overlap. Standard overlap is 6".
- Eave trim (drip edge): Total eave length ÷ 10'. Add 10%.
- Gable trim (rake): Total rake length ÷ 10'. Add 10%.
- Valley trim: Valley length ÷ 10'. W-valley or open valley flashing.
Material Cost Comparison
| Panel Type | Material/sqft | Installed/sqft | Lifespan |
|---|
| Standing Seam | $4-$8 | $8-$16 | 40-70 years |
| Corrugated | $1.50-$3.50 | $4-$8 | 25-40 years |
| R-Panel/PBR | $2-$4 | $5-$10 | 30-50 years |
| 5-V Crimp | $2-$4 | $5-$9 | 25-40 years |