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Roofing Calculator
Enter your roof footprint and pitch. The calculator converts that to actual roof surface, then into squares, shingle bundles, underlayment rolls and ridge cap — the units a supplier will quote against.
How the roofing math works
Roofers work in squares, where one square is 100 square feet of roof surface. Every quantity on a roofing order — shingles, underlayment, starter, ridge cap — is priced per square, so the first job is converting your measurements into that unit.
The critical step is pitch. Your roof covers more surface than its footprint, because it slopes. A 6/12 pitch multiplies the footprint by about 1.118; a 12/12 pitch multiplies it by about 1.414. Skipping the pitch multiplier is the mistake that leaves a job short by several squares, and it gets worse the steeper the roof.
Architectural shingles are typically packaged three bundles to the square, so a 24-square roof needs about 72 bundles. Heavier designer shingles sometimes run four or five bundles per square — always check the wrapper rather than assuming three.
Ridge cap and starter strip are measured in linear feet, not squares, and they are easy to forget. So is underlayment, which is sold by the roll with its own coverage rating.
What throws the estimate off
Valleys, hips and dormers all add cut waste. A simple gable roof might run 5% waste; a roof with several hips and valleys can run 10–15%.
Tear-off changes the job, not the shingle count — but it changes the dumpster, the labour and sometimes the decking. If the existing deck is soft anywhere, budget sheathing.
This is one of the few projects where the estimate should not decide whether you DIY. Roofing is fall-height work with real consequences, and most jurisdictions require a permit and inspection.
Roofing calculator FAQ
What is a roofing square?
One roofing square equals 100 square feet of roof surface. Shingles, underlayment and labour are all quoted per square, so converting your measurements into squares is the first step in any roofing estimate.
How does roof pitch change the amount of shingles?
Pitch multiplies your footprint into actual sloped surface. A 6/12 pitch adds about 12% over the flat footprint, and a 12/12 pitch adds about 41%. Ignoring the multiplier is the most common reason a roofing order comes up short.
How many bundles of shingles are in a square?
Three bundles per square for most architectural and three-tab shingles. Heavier designer profiles can run four or five bundles per square, so check the packaging before ordering.
How much waste should I allow for roofing?
Around 5% on a simple gable roof, and 10–15% on a roof with multiple hips, valleys or dormers, where more shingles get cut on an angle.
Other project calculators
Every calculator on this site works the same way — enter real measurements, get quantities you can hand to a supplier.
- Fence Calculator — Enter your run length, height and post spacing to get exact post, rail, picket and concrete counts, plus a material cost estimate
- Flooring Calculator — Enter room dimensions to get square footage, waste allowance and the number of boxes to buy for laminate, vinyl or hardwood
- Paint Calculator — Enter room dimensions, coats and door and window openings to get the exact number of gallons needed for walls, ceiling and trim
- Deck Calculator — Enter deck size, board width and joist spacing to get decking board counts, joists, beams, footings and fastener quantities
- Drywall Calculator — Enter room dimensions and sheet size to get the number of drywall sheets, joint compound, tape and screws needed, with waste included
- Wainscoting Calculator — Enter wall length and panel height to get panel, chair rail, baseboard and cap moulding quantities plus a material cost estimate
Working through a whole project? The full project calculator keeps all seven in one place, and the in-depth guides cover estimating materials accurately and reducing material waste.