A metal roof is counted by the panel, not the bundle. Each panel covers a set width and runs the length of the slope, so the job is the roof area divided by one panel’s coverage, plus waste. The one number people get wrong is the coverage width. Here is the whole method.
How many panels
First get the real roof area — footprint × the pitch factor (√(rise² + 12²) ÷ 12), because the roof slopes. Then divide by one panel’s coverage (coverage width × panel length) and add waste. A 1,300 sq ft roof in 36 in × 12 ft panels (36 sq ft each) needs about 36 panels — order ~40 with 10% waste.
Coverage width, not overall width
Panels overlap, so the coverage (net) width is less than the panel’s overall width — use the coverage figure or you come up short.
| Profile | Coverage width |
|---|---|
| Corrugated / ribbed (R-panel, PBR) | ~36 in (3 ft) |
| 5V-crimp | ~24 in |
| Standing seam | ~16 in (12–19 in) |
Metal Roof Calculator (Tin & Steel)
Enter your footprint, pitch and panel width for the panels, screws and cost — exposed-fastener or standing seam.
Exposed fastener vs standing seam
Exposed-fastener panels (corrugated, R-panel) screw through the face — cheaper and faster, but the exposed screws and their gaskets are the long-term wear point. Standing seam hides the fasteners under interlocking seams — pricier but longer-lived. The type changes the coverage width and the fastener count.
How many screws
For exposed-fastener panels, budget about 80 screws per square (100 sq ft) — roughly one every 12–18 in along the purlins, plus the laps. A 1,300 sq ft roof is around 1,050 screws. Standing seam uses far fewer visible fasteners because concealed clips hold the panels.
What a metal roof costs
Installed, exposed-fastener steel runs roughly $4–$8 per square foot($400–$800 per square); standing seam more, about $10–$16 per square foot. Materials alone are a fraction — corrugated steel around $1–$3 per sq ft, standing seam $4–$8. Enter a price per square and a labor rate for a full estimate.
Steel, tin or aluminum?
The panel count is the same whatever the metal — only the price and longevity change. “Tin roof” today usually means galvanized or Galvalume steel; aluminum resists coastal corrosion; both come in the same corrugated and standing-seam profiles. Size the panels here, then price them for your chosen metal.