Roofing Calculator
Calculate roofing squares, shingle bundles, and underlayment needed.
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How to Calculate Roofing Materials
Roofing is one of the most important home systems to size correctly. Too few materials means a mid-project delay; too many means wasted money. The roofing calculator accounts for roof pitch — the key factor that makes actual roof area larger than the ground footprint below it.
The Pitch Factor
A pitched roof is larger than its footprint because the surface slopes upward. The pitch factor converts footprint area to actual sloped roof area. For a 6/12 pitch (standard): multiply by 1.118. For an 8/12 pitch: multiply by 1.202. A 50×30 house with 6/12 pitch: 1,500 sq ft × 1.118 = 1,677 sq ft actual roof area.
Roofing Squares
The roofing industry measures material in "squares" — one square = 100 square feet. The 1,677 sq ft example = 16.77 squares. Add 15% waste: 19.3 squares. Round up to 20 squares to order. Standard architectural shingles: 3 bundles per square, so 60 bundles total.
Other Materials
Beyond shingles, a roof job needs: synthetic underlayment (1 roll per square typically), ice and water shield for eaves and valleys (~2 squares worth), ridge cap shingles (1 bundle per 35 linear feet of ridge), roofing nails (2 lbs per square), and ridge vent or ventilation. Drip edge is sold by linear foot and runs the perimeter of the roof edge.
Shingle Types
3-tab asphalt shingles are the entry-level option at $1.50–$2.50/sq ft and last 15–20 years. Architectural (dimensional) shingles at $2.50–$4/sq ft last 25–30 years and look better. Impact-resistant shingles qualify for insurance discounts in hail-prone areas. Metal roofing lasts 50+ years but costs $5–$15/sq ft installed.
Frequently Asked Questions
One roofing square = 100 square feet of roof surface area. It's the standard unit used for pricing materials and labor. A 2,500 sq ft roof = 25 squares.
Standard and architectural asphalt shingles: 3 bundles per square. Some heavier premium products: 4 bundles per square. Always check the bundle packaging for the exact coverage area.
Use a level and tape measure in the attic or on the roof. Place a 12-inch level horizontally on the roof surface. Measure the vertical rise from the end of the level to the roof surface — that is your pitch in X/12 format. A rise of 6 inches = 6/12 pitch.
A typical asphalt shingle re-roof on a 1,500–2,500 sq ft home runs $5,000–$12,000 installed. Metal roofing: $10,000–$30,000. Tile: $15,000–$50,000+. Prices vary significantly by region and roof complexity.
Most building codes allow one layer of new shingles over one existing layer (not two). Reroofing over old shingles saves on labor and disposal costs but adds weight. A full tear-off is better practice as it lets you inspect and repair the decking and start with a flat surface.