Roofing Calculator

To calculate roofing materials: (1) Determine the building's ground footprint area in square feet including eave and rake overhangs. (2) Multiply footprint area by the roof pitch slope factor (e.g., 1.202 for 8/12 pitch, 1.118 for 6/12 pitch) to find true sloped roof surface area. (3) Add a 10% to 15% waste factor for hips, valleys, and starter strips. (4) Divide gross roof area by 100 to get Roofing Squares (1 Square = 100 sq ft). (5) Multiply roofing squares by 3 to determine total asphalt shingle bundle count.

To calculate your true roof surface area: Multiply the building footprint area (Length × Width in feet including 1-2 ft eave/rake overhangs) by the roof pitch slope multiplier. The pitch multiplier formula is Multiplier = √(1 + [Pitch Rise / 12]²). Standard pitch multipliers: 4/12 pitch = 1.054; 6/12 pitch = 1.118; 8/12 pitch = 1.202; 10/12 pitch = 1.302; 12/12 pitch = 1.414. For example, a 2,000 sq ft ground footprint with an 8/12 pitch has a true roof area of 2,000 × 1.202 = 2,404 sq ft.

Using our free roofing calculator square feet tool (usable as an instant web roofing calculator app), enter ground footprint dimensions and overhangs. Select pitch slope to compute true sloped surface area. Sizing works for asphalt shingles (3 bundles per square) as well as a metal roofing calculator (standing seam panels). Enter your cost per square to get accurate roofing calculator cost estimates.

In the roofing industry, a "square" is a standardized unit of measurement equal to exactly 100 square feet (9.29 m²) of roof surface area.

For standard 3-tab and architectural asphalt shingles, there are 3 bundles per roofing square. For heavy laminated or specialty designer shingles, there may be 4 bundles per square.