Roofing Calculator

A roofing square is the standard industry unit of area measurement. It equals exactly 100 square feet of roof surface. For example, a roof with a surface area of 1,800 square feet is referred to as an 18-square roof.

For typical architectural or 3-tab shingles, it takes exactly 3 bundles to cover 1 roofing square (100 square feet). That means each individual bundle contains enough shingles to cover about 33.3 square feet.

A steeper slope means a larger roof surface area for the exact same building footprint. The calculator uses the roof pitch (expressed as rise over 12 inches of run) to compute a slope multiplier, expanding the flat footprint to the actual sloped area.

Order a 10% waste factor for simple gable roofs with few obstructions. For complex roofs featuring hips, valleys, dormers, and multiple chimney penetrations, increase your waste margin to 15% or 20% to cover cuts and starter courses.

Underlayment is the protective barrier laid directly onto the plywood deck. A standard roll of traditional #15 felt covers 400 square feet (4 squares), while modern synthetic underlayment rolls usually cover 1,000 square feet (10 squares).