Formula and input notes
Roof area = plan length × plan width × slope factor × (1 + waste ÷ 100); roofing squares = area ÷ 100
| Input | Practical note |
|---|---|
| Slope factor | The slope factor converts horizontal plan area to sloped surface area. Derive it from the actual pitch rather than choosing it from appearance. |
Worked metal roof example
Metal Roof Calculator example: 50.8 ft × 25.8 ft × 1.12 × 1.1 = 1,614.71 ft², or 16.15 roofing squares.
Read squares and sloped area
Use calculated squares for budget comparison, then obtain a panel-by-panel layout and trim schedule from the system supplier.
Geometry and accessories outside the total
Panel rib width, sidelap, endlap, stock length, valleys, hips, rake cuts, clips, fastener pattern, and trim lengths drive real waste.
Questions specific to this calculation
Does the result include panel sidelap, endlap, and trim?
Enter plan dimensions and slope factor for each roof plane. Panel takeoff also requires eave-to-ridge length and usable panel coverage, which this area tool does not request.