Roofing Calculator
Calculate the sloped roof surface area, roofing squares, and shingle bundles needed for a flat or pitched roof.
ft
ft
%
Extra material for cuts, overlaps, and mistakes (10% is typical)
Roofing Squares Needed
13.20
(1 square = 100 sq ft)
≈ 40 shingle bundles
Sloped surface area: 1200 sq ft | With waste: 1320 sq ft
How to Use the Roofing Calculator
Enter your roof's ground footprint (length × width). If your roof is flat or you already know the actual sloped surface area, use the "Flat / Simple Roof" mode. For a pitched roof, switch to "Pitched Roof" and enter the pitch angle in degrees — the calculator divides the flat footprint area by the cosine of that angle to find the true sloped surface area that needs covering, since a steeper roof has more actual surface area than its footprint suggests.
Roofing material is sold and measured in "squares" — a standard roofing industry unit equal to 100 square feet of roof surface. Once the total area (including a waste allowance for cuts, overlaps, and mistakes) is calculated, it's divided by 100 to get the number of squares, and multiplied by 3 to estimate the number of standard shingle bundles needed (most asphalt shingles are packaged 3 bundles per square).
Example
A 40 ft × 30 ft footprint (1,200 sq ft) with a 25° pitch has a sloped area of 1,200 ÷ cos(25°) ≈ 1,324 sq ft. Adding a 10% waste allowance brings the total to about 1,456 sq ft, which is 14.56 roofing squares — roughly 44 shingle bundles.
Common Use Cases
- Estimating how many shingle bundles to buy for a re-roofing project.
- Getting a rough material budget before requesting contractor quotes.
- Comparing material needs between a flat and a pitched roof design.
FAQs
What is a roofing "square"?
A roofing square is a standard industry unit equal to 100 square feet of roof surface area. Contractors and material suppliers use squares (not square feet) when quoting and pricing roofing jobs.
How much waste allowance should I use?
10% is a common default for a straightforward roof. Roofs with many hips, valleys, dormers, or a complex shape often need 15-20% to account for extra cuts and offcuts.
Is this a substitute for a professional roofing estimate?
No. This calculator gives a reasonable material estimate for planning purposes, but actual roofing jobs should be measured and quoted by a licensed roofing contractor, who can account for the roof's exact shape, underlayment, flashing, and local building code requirements.