Roofing Calculator

Standard 3-tab asphalt shingles and most architectural/dimensional shingles require 3 bundles per square. Each bundle covers approximately 33 sq ft, so three bundles cover 100 sq ft (1 square). Some premium architectural shingles are heavier and come 4 bundles per square — always check the manufacturer's spec sheet for the specific product you are buying. This calculator uses the 3-bundle standard.

The footprint area (ceiling below) is not the same as the actual roof surface. A steep pitch creates a longer slope — more surface to cover with shingles. A 6:12 pitch adds about 11.8% more area than the footprint; a 12:12 pitch adds 41.4% more. This calculator applies the correct pitch adjustment factor (√(1 + (pitch/12)²)) so your material estimate is based on the true sloped area, not just the floor plan.

Add 10% for simple rectangular gable roofs. Use 15% for hip roofs, which have diagonal cuts at all four corners. Use 15–20% for complex roofs with multiple valleys, dormers, or irregular geometry. Starter strips, ridge cap shingles, and waste from cutting around chimneys, skylights, and vents all consume additional material. It is far cheaper to order one extra bundle upfront than to make a second trip for a partial order.

Yes — underlayment covers the same sloped roof area as shingles. Order the same number of squares of underlayment as your shingle estimate. Standard #15 felt comes in 4-square rolls; synthetic underlayment rolls vary (10 squares is common). Add 10% overlap between rolls when calculating how many rolls you need — most manufacturers specify 2–4 inch horizontal overlaps and 6-inch head-lap at vertical seams.

Measure the building footprint from the ground (length and width). Use a pitch gauge, smartphone app, or the 12-inch level method to determine the pitch (see the Roof Pitch Calculator). Multiply footprint area by the pitch factor to get roof area. For a gable roof with two equal slopes, the full width × full length gives the total footprint. For hip roofs, the same formula works — the pitch factor accounts for the slope regardless of roof shape.

3-tab shingles are flat with cutouts giving three equal tabs per strip — lighter, thinner, and cheaper. Architectural (dimensional) shingles have a thicker, layered appearance that mimics wood shake or slate — heavier, longer-lasting (typically 30-year vs 20-year warranty), and the industry standard for new construction. Both use 3 bundles per square at standard coverage. Architectural shingles cost 20–30% more per square but offer better wind resistance and curb appeal.

Material costs for architectural asphalt shingles run $100–$160 per square (3 bundles × $35–$55 per bundle). A 20-square roof is $2,000–$3,200 in shingles alone. Add underlayment ($15–$25 per square), nails, ridge cap, and flashing. Professional installation adds $150–$350 per square for labor, bringing the total to $300–$500 per square installed. A 20-square roof: $6,000–$10,000 fully installed. Metal roofing runs $400–$900 per square installed. Always get three quotes — prices vary significantly by region and contractor.