Roofing Calculator

How This Roofing Calculator Works

This calculator chains the core roofing math: footprint → surface area → roofing squares → material quantities. All calculations run on the shared RoofCalcWorks calculation engine, the same engine behind every individual calculator on this site.

Formulas

• Footprint = (Length + 2 × Overhang) × (Width + 2 × Overhang)
• Roof Surface Area = Footprint × √(1 + (Rise / Run)²)
• Roofing Squares = Roof Area ÷ 100, with waste: × (1 + Waste %)
• Shingle Bundles = Squares × 3 (at 33.3 sq ft/bundle), rounded up
• Underlayment Rolls = Adjusted Area ÷ 400 sq ft/roll, rounded up

Worked Example

50 ft × 30 ft, 1 ft overhang, 6/12 pitch, 10% waste: footprint = 52 × 32 = 1,664 sq ft; surface area ≈ 1,860 sq ft ≈ 18.6 squares → 20.5 squares with waste → 62 bundles, 5 rolls of underlayment.

What You Need

The building's outside length and width, its roof pitch and the roof type. Overhang is optional — add it if you want the eaves included. If you don't know the pitch, measure it in the attic or use our Roof Pitch Calculator first.

Assumptions & Limitations

Models a simple rectangular roof. Roof type is recorded for future refinement — in this version the geometry math is identical for gable, hip, shed and flat shapes. Complex roofs should be calculated section by section. Coverage values are configurable; actual product coverage depends on the manufacturer.