Roofing Square Calculator
Roofing squares, bundles & underlayment
Enter roof dimensions
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Formula & explanation
The pitch factor adjusts the flat footprint for the sloped roof area. A roofing "square" is 100 sq ft of roof coverage. Architectural shingles typically require 3 bundles per square (some starter/waste included in your allowance). Underlayment rolls cover about 2 squares each.
Example calculation
40 × 30 ft house, 6/12 pitch, 15% waste:
Footprint = 1,200 sq ft × 1.118 (6/12 factor) = 1,342 sq ft roof. With 15% waste = 1,543 sq ft = 15.4 squares → 47 bundles, 8 underlayment rolls.
Buying & project-planning tips
- Always buy full bundles — partial bundles usually can't be returned.
- Include starter shingle and hip/ridge cap in your bundle count or add ~10% more.
- Steep roofs (8/12+) cost more in labor and may need special underlayment per code.
- Order drip edge and ice-and-water shield separately for valleys and eaves in cold climates.
- A second layer over existing shingles is not recommended and may void warranties — tear off first.
Frequently asked questions
What is a roofing square?+
One roofing square = 100 square feet of roof area. Shingles are sold by the square, with typically 3 bundles per square for standard architectural shingles.
How much waste should I add for roofing?+
15% is typical for a standard gable roof. Add 20%+ for roofs with many valleys, dormers, or hips — lots of cuts mean more waste.
Does this calculator include labor?+
No — it estimates materials only. Labor is usually priced per square and varies widely by region and roof complexity.
Do I need a permit to replace my roof?+
Most jurisdictions require a permit for roof replacement. Check with your local building department, and confirm your roofer is licensed and insured.