Tool
Roofing Calculator
Estimate roof surface area from footprint dimensions and pitch.
Construction Calculators
What this tool does
Estimate total roof surface area by applying a pitch factor to the building footprint. Helpful before ordering shingles and underlayment.
How to use
- Enter roof length and width in feet.
- Enter pitch as rise in inches per 12 inches of run.
- Review the calculated roof area in square feet.
Examples
40x30 roof at 4/12 pitch
Input: Length: 40 ft, Width: 30 ft, Pitch: 4
Output: Roof area: 1249.00 sq ft
Footprint 1,200 sq ft multiplied by pitch factor √(1 + (4/12)²).
Assumptions
- Roof footprint is rectangular.
- Pitch factor uses √(1 + (rise/12)²) applied to footprint area.
- Does not subtract dormers, valleys, or penetrations automatically.
Common use cases
- Estimate roofing area before shingle orders
- Compare material needs across pitch options
- Plan underlayment and ice barrier quantities
FAQ
How do I measure pitch?
Pitch is rise over a 12-inch run. A 4/12 pitch rises 4 inches for every 12 inches horizontally.
Does this include overhangs?
Include eave and rake overhangs in your length and width for better material estimates.
Can I use this for complex roofs?
Simple gable-style footprints work best. Break complex roofs into sections.
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Last reviewed: 2026-05-23