Roofing Calculator
Calculate roofing squares and shingle bundles, and convert roof pitch to degrees.
Results
Enter the rise and run in feet (for example, 7.5 ft of rise over a 15 ft half-span), or type an angle in degrees. The other values update as you type.
Pitch Conversions
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. Measure the footprint to the outside of the eaves, not the walls, so overhangs are included.
The multiplier comes straight from the geometry: it is √(1 + (rise ÷ run)²), the length of the sloped rafter divided by its horizontal run. Common values: 3/12 = 1.031, 4/12 = 1.054, 6/12 = 1.118, 8/12 = 1.202, 10/12 = 1.302, 12/12 = 1.414. The pitch converter above calculates it for any pitch.
Roof Pitch, Angle, and Slope
American roofers describe pitch as inches of rise per 12 inches of horizontal run, so a 6/12 roof climbs 6 inches for every foot it runs inward. To find it from measurements, pitch = (rise ÷ run) × 12: a roof that rises 7.5 feet over a 15-foot half-span is (7.5 ÷ 15) × 12 = 6/12. The angle is arctan(rise ÷ run): 3/12 = 14.0°, 4/12 = 18.4°, 5/12 = 22.6°, 6/12 = 26.6°, 7/12 = 30.3°, 8/12 = 33.7°, 9/12 = 36.9°, 12/12 = 45°. Slope as a percentage is simply rise ÷ run × 100, so 6/12 is a 50% slope.
To measure an existing roof, hold a level horizontally with one end touching the roof deck, mark 12 inches along it, and measure straight down to the roof: a 7-inch drop is a 7/12 pitch. You can take the same reading in the attic against the underside of a rafter, which is safer. Most US homes fall between 4/12 and 9/12, with 6/12 the most common; anything steeper than about 8/12 generally calls for roof jacks and fall protection, and contractors charge more for it.
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 come 3 bundles per square: 19.3 × 3 = 58 bundles, or 60 if you order by whole squares.
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. Hold a level horizontally with one end touching the roof surface, mark 12 inches along it, and measure straight down to the roof. That rise is your pitch in X/12 format: a rise of 6 inches = 6/12 pitch.
Angle = arctan(rise ÷ run). For a 6/12 pitch, arctan(6 ÷ 12) = 26.6°. Other common values: 4/12 = 18.4°, 8/12 = 33.7°, 12/12 = 45°. To go the other way, rise per 12 inches = tan(angle) × 12, so a 30° roof is about a 6.9/12 pitch. The pitch converter on this page does both directions.
Asphalt shingles are installed normally on roofs of 4/12 and steeper. From 2/12 to 4/12 they are allowed with a double layer of underlayment, and below 2/12 they cannot be used. Low-slope roofs need standing-seam metal or a membrane such as TPO, EPDM, or PVC.
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, roof complexity, and pitch, since steeper roofs are slower and need safety equipment.
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.