Roofing Calculator

How it works

Roofers measure roof area in "squares" — one square equals 100 square feet of roof surface. A typical American home has 20-30 squares of roof. Shingles are sold by the bundle (covering ~33 ft²) and three bundles typically cover one square (architectural shingles); 4 bundles per square may be needed for some 3-tab styles.

The roof surface is larger than the building footprint because of the pitch (slope). Pitch is expressed as rise-over-run: a 6/12 pitch rises 6 inches for every 12 inches of horizontal run, which gives a slope factor of √(6² + 12²) / 12 = 1.118. So a 30 × 40 ft (1,200 ft²) footprint with a 6/12 gable roof is actually 1,200 × 1.118 = 1,342 ft² of roof surface = 13.4 squares.

This calculator handles simple gable roofs (two sloped sides meeting at a ridge). For hip roofs (sloped on all four sides), the math is similar — same footprint, same pitch, same slope factor. For complex roofs with valleys, dormers, hips, and turrets, manual takeoff or specialty software is more accurate.

Always order 10-15% extra. Cuts at hips, valleys, and the ridge produce waste; gables need starter shingles along the eaves; ridge caps are typically a separate count. A typical installer will throw away 5-10% of materials from cuts alone.

Beyond shingles, a re-roof needs felt or synthetic underlayment, drip edge metal, ice-and-water shield in cold climates, ridge vents, pipe boots for plumbing vents, and possibly new flashing. Underlayment is sold by the roll covering 4 squares; buy enough for the whole roof. Materials typically run $200-400 per square; add labor of $200-500 per square depending on region and roof complexity.

Lifespan matters when budgeting. 3-tab asphalt shingles last 15-20 years; architectural (laminated) shingles 25-30 years; metal roofs 40-70 years; clay tile 50+ years. Premium materials cost 2-4× as much upfront but the per-year cost is often lower.