Roofing Calculator
Calculate exactly how many squares and bundles of shingles you need for your roof based on footprint and pitch.
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Roof Pitch & Area
Measure your home's total footprint at ground level. Our calculator uses the roof's slope (Pitch) to easily determine the true sloped surface area.
How to Use the Roofing Calculator
Calculating the true surface area of a sloped roof from the ground can be dangerous. Our calculator uses standard geometry (the Pythagorean theorem) to determine your true roof area using only flat measurements from the ground.
- Measure the footprint: Measure the length and width of the house from the outside walls, including the roof overhangs (usually 1 to 2 feet past the walls).
- Determine the pitch: Select the steepness of your roof. Standard residential roofs are typically 4/12 or 6/12.
- Add a waste factor: Select 10% for standard roofs or 15% for complex roofs with lots of valleys.
- Get your bundles: The calculator outputs the exact number of standard shingle bundles you need to buy at the store.
Roofing Calculation Formula
Because a roof is sloped, its actual surface area is greater than the flat area beneath it. We use Pitch Multipliers to easily scale the flat area to the true sloped area.
Step 1: Calculate Flat Area
Flat Area = Length (ft) × Width (ft)
Step 2: Apply Pitch Multiplier
True Area = Flat Area × Pitch Multiplier
(e.g., A 6/12 pitch has a multiplier of 1.118)
Step 3: Calculate Squares & Bundles
Roofing Squares = True Area ÷ 100
Bundles = Squares × 3
Roofing Example Calculation
You have a rectangular home that is 60 feet long and 40 feet wide (including overhangs). The roof has a standard 6/12 pitch, and you are adding 10% waste.
- Flat Area: 60 × 40 = 2,400 sq ft.
- True Area (6/12 pitch): 2,400 × 1.118 = 2,683 sq ft.
- Add Waste (10%): 2,683 × 1.10 = 2,951 sq ft.
- Squares: 2,951 ÷ 100 = 29.5 squares.
- Bundles: 29.5 × 3 = 88.5 (round up to 89 bundles).
Conclusion: You need to purchase 89 bundles of shingles.
Tips for Replacing Your Roof
- Don't forget the starter shingles: You will need specific "Starter" shingles for the eaves and rakes (the perimeter of the roof) to seal the first row. These are sold linearly, not by the square.
- Ridge caps: You will also need special ridge cap shingles to cover the peak of the roof. Do not try to fold standard architectural shingles over the peak, as they will crack over time.
- Underlayment: You will need synthetic underlayment or tar paper to cover the entire bare wood deck before applying shingles. One roll of synthetic underlayment usually covers 10 squares (1,000 sq ft).
Frequently Asked Questions
What is a roofing square?
In the roofing industry, a 'square' is a unit of measurement equal to exactly 100 square feet of roof surface area.
How many bundles of shingles are in a square?
For standard architectural and 3-tab asphalt shingles, there are exactly 3 bundles per roofing square. Therefore, one bundle covers approximately 33.3 square feet.
What is roof pitch?
Roof pitch is the steepness or slope of the roof, represented as a ratio of 'rise over run'. A 6/12 pitch means the roof rises 6 inches vertically for every 12 inches it extends horizontally. The steeper the pitch, the higher the multiplier required to calculate surface area from the flat footprint.
How much waste should I add for roofing?
For a simple gable roof with no valleys or dormers, 5% to 10% waste is standard. For a complex roof with multiple hips, valleys, and dormers, you should add a 15% waste factor to account for the shingles you must cut to fit the angles.