Roofing Calculator
Estimate roof surface and whole material packages from horizontal area, uniform pitch and waste.
Formula
Roof area = plan area × √(1+(pitch/12)²); order area = roof area × (1+waste/100); packages = ceil(order area/coverage).
Horizontal roof footprint: 1,000 ft² · Coverage per package: 33.33 ft² · Roof surface area ≈ (1,000 ft² × 0.09290304 m²/ft²)×sqrt(1+((6)÷12)^2) · Area including waste ≈ (103.8687564)×(1+(10)÷100) · Whole packages ≈ ceil((114.255632)÷(33.33 ft² × 0.09290304 m²/ft²)-8.881784197001252e-16×max(1,abs((114.255632)÷(33.33 ft² × 0.09290304 m²/ft²))))
How to use
- Enter horizontal roof footprint including eaves.
- Enter rise per 12 units of run and waste percentage.
- Enter package coverage from the product label and read totals.
Examples
- 100 m² at 9:12 gives 125 m²; 10% waste and 5 m² per pack need 28 packs.
Frequently asked questions
Is this the house floor area?
Use the horizontal roof footprint including overhangs; it can exceed floor area.
What if roof sections have different slopes?
Calculate each section separately and combine material needs.
Are ridges and flashing included?
No. Caps, flashing, underlay overlaps and accessories need separate takeoffs; coverage is user supplied.
Sources
Updated: