π Roofing Calculator
Calculate roofing squares, shingle bundles, and materials needed.
Roofing Squares (with waste)
How to Use This Calculator
Enter the building footprint length and width (not the sloped roof surface). The calculator applies the pitch multiplier automatically to give you the actual roof surface area. Set your waste percentage higher for complex roofs with multiple valleys, dormers, or hip sections.
Measure the building footprint, not the roof slope. If your house is 40 feet long and 28 feet wide, those are your numbers regardless of roof pitch.
Choose your roof pitch from the dropdown. A 4/12 pitch (4 inches of rise per 12 inches of run) is the most common in residential construction.
Set your waste percentage. Use 10% for simple gable roofs. Use 15% for hip roofs. Use 20% or more for complex roofs with multiple valleys, dormers, and intersections.
Choose bundles per square. Standard 3-tab shingles use 3 bundles per square. Most architectural or dimensional shingles also use 3 bundles, but some heavy-weight styles use 4. Check your product label.
Roofing Area Formula
A 4/12 pitch has a multiplier of about 1.083. A 6/12 pitch uses 1.118. A steep 12/12 pitch (45 degrees) uses 1.414, meaning you need 41% more material than the footprint suggests.
Example Projects
Tips for Your Project
Always add at least 10% for waste, and more for complex roofs. Valleys, hips, and ridge lines require cuts that generate significant scrap. A ridge cap also takes 1 bundle per 35 linear feet of ridge, and starter strip shingles add about 1 bundle per 100 linear feet of eave. Order all your shingles at once from the same production run to avoid color variation between bundles.
For underlayment, figure one roll per 4 squares of roof. Most felt paper or synthetic underlayment rolls cover 400 square feet. Drip edge runs along every eave and rake edge, so measure your total perimeter and buy that in linear feet. Ice and water shield goes along the lower 3 to 6 feet of the eaves and in every valley, so factor those areas in separately.
Frequently Asked Questions
What is a roofing square?
A roofing square = 100 square feet of roof surface. All roofing materials (shingles, felt, etc.) are sold by the square.
How many bundles of shingles per square?
Standard 3-tab shingles: 3 bundles per square. Architectural shingles: typically 3β4 bundles per square. Shingle weight varies by brand.
What is roof pitch and how does it affect area?
Roof pitch is the rise in inches per 12 inches of horizontal run (e.g., 4/12). Steeper roofs have more surface area than the footprint suggests. A multiplier accounts for this.
What is the waste factor for roofing?
Add 10% for simple gable roofs; 15% for hip roofs; 20%+ for complex roofs with many valleys, hips, and dormers.
How much underlayment do I need?
Roofing felt/underlayment covers the same area as shingles, typically sold in 4-square rolls (400 sq ft). You'll need approximately the same number of squares.