Roofing Square Calculator

Enter your roof’s length, width and pitch, or the roof area if you already know it, and this roofing square and shingle calculator gives you the true roof surface area, the number of roofing squares, squares with waste added, and the shingle bundles to order. Results update as you type. No signup.

How the roofing square and shingle calculator works

A roofing square is 100 square feet of roof surface. Contractors quote in squares, shingle manufacturers package by the square, and most labor rates are set per square, so it is the unit that every roofing estimate is built on. A shingle calculator and a roofing square calculator do the same job: work out how many squares of surface you have, then convert that into the bundles of shingles you need to buy. This page does both from four inputs.

The variables

• Roof length is the long dimension of the house measured along the ridge, from one gable end to the other, including any overhang at the eaves.
• Roof width is the short dimension measured flat on the ground from eave to eave. Together, length and width give the footprint: the area the roof would cover if it were flat.
• Roof pitch is how steep the roof is, written as inches of rise per 12 inches of run. Each pitch in the dropdown carries a multiplier that converts flat footprint into sloped surface area. If you do not know your pitch, measure it with the roof pitch calculator first.
• Waste factor is the percentage of extra material you buy to cover cut shingles at edges, hips, valleys and around penetrations. 10% is the standard allowance for a simple gable roof.

If you already have a roof surface area from a measurement, a satellite roof report or our roof area calculator, switch to the “I know the roof area” mode and skip straight to squares and bundles.

Formula 1: flat footprint area

footprint = length × width

A 40 by 30 foot house has a 1,200 square foot footprint. For an L-shaped or T-shaped house, break the roof into rectangles, run each one through the calculator, and add the results together. Do not use the interior living area from a listing: it excludes overhangs and, on a two-story house, counts floor space that sits under the same roof twice.

Formula 2: true roof surface area

roof area = footprint × pitch multiplier

Because a roof slopes, its surface is larger than the footprint underneath it. The pitch multiplier is the ratio of sloped length to horizontal run, which is √(rise² + run²) ÷ run. At 6:12 the multiplier is 1.118, so a 1,200 square foot footprint becomes 1,342 square feet of shingled surface. At 12:12 the multiplier is 1.414 and the same footprint becomes 1,697 square feet. This step is where most do-it-yourself estimates go wrong: measuring the footprint and forgetting the pitch under-orders by 5 to 40 percent.

Formula 3: roofing squares

squares = roof area ÷ 100

1,342 square feet is 13.4 squares. Squares are quoted to one decimal place by most contractors. This is the figure that matters for comparing bids, because a quote of “$450 per square” only means something once you know how many squares you have.

Formula 4: squares with waste

squares with waste = squares × (1 + waste% ÷ 100)

13.4 squares at 10% waste is 14.8 squares. Waste covers the shingles that get cut at rakes, valleys, hips and around vents, chimneys and skylights. Some of the offcuts get reused, but many cannot be. A simple gable with no penetrations can get away with 5 to 10 percent. A hip roof, or any roof with multiple valleys and dormers, usually needs 15 percent, and very cut-up roofs can need 20 percent.

Formula 5: shingle bundles

bundles = squares with waste × 3, rounded up to a whole bundle

This calculator assumes 3 bundles per square, which is the standard for three-tab shingles and the great majority of architectural (laminated) shingles. 14.8 squares becomes 44.4 bundles, so you order 45. Some heavyweight designer and luxury shingles are packed at 4 or 5 bundles per square. If your product’s wrapper says otherwise, multiply your squares with waste by the bundles-per-square figure printed on it instead.

What changes the number

• Pitch is the biggest lever. Between a 4:12 and a 10:12 roof the multiplier moves from 1.054 to 1.302, a 24 percent difference in material on the same footprint. Guessing the pitch is the most common source of large errors.
• Roof shape sets the waste. Hips, valleys and dormers all generate cut pieces. If your roof has more than two valleys or any hips, raise the waste factor from 10 to 15 percent.
• Overhangs count. Eave and rake overhangs of 12 to 24 inches on each side can add 150 to 250 square feet to a typical house. Measure the roof edge, not the wall.
• Sections add up. Attached garages, porches and bump-outs each have their own footprint and often their own pitch. Calculate them separately.

What is not included

Bundle counts here cover field shingles only. You will also need starter strip along the eaves and rakes (sold per linear foot), hip and ridge cap shingles (sold per linear foot of hip and ridge), underlayment, drip edge, ice and water shield in cold climates, and roofing nails. A typical 15-square roof needs roughly 150 linear feet of starter and 50 to 80 linear feet of ridge cap. Those items add 10 to 15 percent to the material bill on top of the shingles.

From squares to cost

Once you have squares with waste, the estimate is a straightforward multiplication. Installed asphalt shingle roofing in most of the country runs between $350 and $600 per square for standard architectural shingles, with tear-off, steep pitch and complex shapes pushing the figure up. The roof replacement cost guide breaks that range down by material, region and roof complexity so you can turn your square count into a realistic budget before you talk to a contractor.

Roofing squares by house size

Squares and bundles for common footprints at 10% waste and 3 bundles per square. Footprint is the flat area under the roof including overhangs.