Roofing calculator
Metal roofing calculator
Pitched roof area and whole metal-panel quantity using stated panel coverage.
Calculator result and formula
Metal panels to order: 21 panels
Formula: L × W × √(1 + (rise ÷ 12)²) × (1 + waste) ÷ net coverage
Formula ID: ROOF-METAL-001 · Version 1.0.0.
Inputs
- Roof length: Horizontal roof length Default: 30.
- Roof width: Horizontal roof width Default: 20.
- Pitch rise: Rise for every 12 units of run Default: 6.
- Panel coverage: Net coverage of one selected panel Default: 36.
- Waste factor: Allowance for cuts, trim, detail and spares Default: 10.
How this calculator works
This calculator applies roof pitch to horizontal dimensions, then divides the adjusted area by the selected panel's net coverage after a visible allowance.
- Measure the horizontal roof length and width.
- Enter rise per 12 and net coverage for the selected panel profile.
- Confirm panel lengths, trim, fasteners and supplier packaging separately.
Worked example: Example: a 30 ft × 20 ft roof at 6:12 has about 671 ft² of slope-adjusted area. With 10% waste and 36 ft² of panel coverage, it rounds to 21 panels.
Assumptions and limitations
- Roof surface is calculated from a rectangular horizontal footprint and rise-per-12 pitch.
- Coverage must be the selected product's net usable coverage.
- Waste is applied before whole-unit purchase rounding.
Common questions
- Does this estimate trim or fasteners?
- No. Panel coverage only estimates primary roof panels; trim and accessories require their own takeoff.
- Can all metal panels use the same coverage?
- No. Enter the selected manufacturer's net coverage and account for installation details separately.
Reference notes
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