Roof Area Calculator

Start with building footprint (length × width), then multiply by pitch factor. The pitch factor accounts for the slope increasing surface area. For a 6/12 pitch, multiply footprint by 1.118. Add overhang area (perimeter × overhang depth). This gives total roof plane area. For hip roofs, the calculation is similar but geometry differs. This calculator handles all the math automatically.

The pitch multiplier converts flat area to sloped roof area. Formula: √(1 + (pitch/12)²). A flat roof has multiplier of 1.0; a 12/12 (45°) roof has 1.414—meaning 41.4% more surface area than the footprint. Common values: 4/12=1.054, 6/12=1.118, 8/12=1.202, 10/12=1.302, 12/12=1.414. This significantly affects material quantities and costs.

Add overhang to building dimensions before calculating. Standard overhangs are 12-24 inches (30-60cm). Calculate: (building length + 2×overhang) × (building width + 2×overhang). Then apply pitch multiplier. Overhangs add 5-15% to total roof area depending on building size. Larger buildings have proportionally less overhang impact than smaller structures.

Gable roofs have two sloped sides meeting at a ridge—calculation uses length × sloped width × 2. Hip roofs slope on all four sides with more complex geometry involving triangular and trapezoidal sections. Hip roofs typically have slightly less total area than gable for same footprint but require more labor and materials for hips and valleys. Both calculations included here.

Break complex roofs into simple sections: main roof, dormers, valleys, additions. Calculate each section separately using appropriate pitch factors, then add together. Valleys and dormers add 10-20% complexity. For very complex roofs, use actual measurements or satellite imagery measurement tools. Professional estimators often add 10-15% to calculations for waste and irregularities.

Divide total roof area by 100 to get squares (1 square = 100 sq ft / 9.29 m²). Add 10-15% for waste—more for hip roofs and complex shapes. Standard shingles: 3 bundles per square. Order underlayment, drip edge, ridge caps, and ventilation based on square count and linear measurements. This calculator provides square calculations automatically.