Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Calculate roof surface area, squares, and shingle bundles from your building footprint and roof pitch.
A sloped roof always has more actual surface area than the flat footprint of the building beneath it -- the steeper the pitch, the bigger the difference. This calculator converts your building's flat footprint area into the real roof surface area using the pitch, then converts that into roofing "squares" (100 sqft each, the standard unit roofing materials are sold in) and shingle bundles.
Enter your building's footprint area (length x width of the house, not the roof itself) and the roof's pitch as the rise per 12 inches of run -- a "6/12" pitch means enter 6.
Slope Factor = √(Rise² + 12²) ÷ 12
Roof Area = Footprint Area × Slope Factor
Squares = Roof Area ÷ 100
A flat (0/12) roof has a slope factor of exactly 1 (no extra area). A 6/12 pitch has a slope factor of about 1.118 -- roughly 12% more surface area than the flat footprint. A steeper 12/12 pitch (a 45-degree roof) has a slope factor of about 1.414, 41% more area.
Use this for a quick, single-pitch roof estimate before ordering shingles. If your roof has multiple sections at different pitches or already-measured plane areas, the Roof Area Calculator sums those directly instead. To convert an area you already know into materials without recalculating the pitch, see the Roof Shingle Calculator.
The input is the footprint of the building, meaning the area of the roof as viewed from directly above, not the sloped surface itself. Measure the outside of the house at the walls, then add the roof overhang on each side, because the eaves and rakes extend beyond the walls and also need shingles. For a simple rectangle, multiply length by width including overhangs. If the house has an attached garage or porch under the same roof, include it in the footprint.
Suppose a hypothetical house is 40 by 30 feet at the walls, with a 1-foot overhang on all sides, giving a roof footprint of 42 by 32 = 1,344 square feet. The pitch is 8/12, which gives a slope factor of sqrt(64 + 144) / 12 = sqrt(208) / 12, about 1.2019. The roof area is 1,344 x 1.2019, or roughly 1,615 square feet, which is 16.15 squares. At three bundles per square that is about 49 bundles before waste. Adding waste for a gable roof, commonly in the range of 10 percent, brings it to about 54 bundles. Confirm the waste amount with your roofer.
Roof Area = Footprint Area × √(Rise² + 144) ÷ 12
Squares = Roof Area ÷ 100
To find your pitch, place a level horizontally against the roof surface (or against a rafter in the attic), measure 12 inches along the level, and then measure straight up or down from the 12 inch mark to the roof. That measurement is the rise. From the ground, you can also estimate the pitch from building plans, which usually label it. Be careful when accessing a roof: a steep slope is dangerous, and taking measurements from the attic or from plans is safer than climbing.
A roof job also involves underlayment, drip edge, flashing, ventilation, nails, and possibly ice and water shield in cold climates. Their quantities depend on roof edges, valleys, and local requirements, and are not calculated by this tool.
Roofing has real fall risks and structural considerations. If your roof deck is damaged, or the old layers of shingle limit how many layers may be added, consult a licensed roofer and check your local building code.
100 square feet -- the standard unit roofing materials (shingles, underlayment) are measured and sold in throughout the US roofing industry.
3 bundles per square is standard for most asphalt shingles, though this can vary slightly by manufacturer and product line -- always check your specific shingle's coverage.
Because the roof is sloped, not flat -- a sloped surface covering the same footprint has more actual area than a flat one, and the steeper the pitch, the bigger that difference is.
Yes. Shingles cover the eaves and rakes too, so use the footprint that includes them.
Convert the angle to rise per 12 inches by taking 12 times the tangent of the angle. A 30 degree roof is about 6.9/12.
Ridge and hip caps are usually purchased separately, based on the length of ridges and hips.
You can use the area and squares. Metal panels are sold by panel size, so convert the area to panel counts separately.