Roofing Calculator

A roofing "square" equals 100 square feet (9.29 m²) of roof area. For standard 3-tab shingles, you need 3 bundles per square. Architectural (dimensional) shingles often require 4-5 bundles per square due to heavier weight. Each bundle covers approximately 33.3 sq ft (3.1 m²). Always check manufacturer specifications as coverage varies by product. Include 10-15% extra for waste, valleys, hips, and ridges.

Steeper roofs have more surface area than the building footprint. A 6/12 pitch adds about 12% to area, while 12/12 (45°) adds 41%. The pitch multiplier formula is √(1 + (pitch/12)²). For a 12×9m (40×30 ft) building, actual roof area ranges from 117 m² (1,264 sq ft) at 4/12 to 158 m² (1,697 sq ft) at 12/12. This significantly impacts material costs and installation labor.

Asphalt shingle bundles: USA $25-50; Canada C$30-60; UK £25-45 (felt tiles more common); Australia A$30-70; India ₹150-400/sq ft for various materials. Metal roofing costs 2-3× more but lasts longer. Clay/concrete tiles vary widely. Installation typically costs 50-100% of material cost. Total roof replacement runs $5-15/sq ft (USA) or equivalent in other regions depending on material choice and complexity.

Break complex roofs into simple shapes: rectangles, triangles, and trapezoids. For hip roofs, calculate two triangular ends and two trapezoidal sides. For dormers, add their roof area to main roof. Valleys and hips need extra for specialty materials—add 10% to total. Use 15-20% waste for complex roofs versus 10% for simple gables. Consider professional measurement for multi-story or steeply pitched roofs for accuracy and safety.

A complete roofing job requires: underlayment (1 roll per square), drip edge (linear feet of perimeter), ice & water shield in cold climates (valleys, eaves), ridge caps (linear feet of ridges/hips), roofing nails (2 lb per square), ventilation (1 sq ft per 150 sq ft attic). Flashing for chimneys, vents, and walls. Budget 20-30% of shingle cost for these additional materials.

Material lifespans vary significantly: 3-tab asphalt shingles last 15-20 years; architectural shingles 25-30 years; metal roofing 40-70 years; clay/concrete tiles 50-100 years; slate 75-150+ years. Climate affects longevity—UV, wind, hail, and freeze-thaw cycles shorten lifespan. Higher quality materials often provide better value despite higher upfront cost. Consider lifespan when comparing total cost of ownership.