Roofing Calculator
Estimate roofing materials for your project — shingles, bundles, underlayment rolls, and total cost. Supports gable, hip, and flat roof shapes with adjustable pitch and waste factors.
How to Use This Calculator
- Select your roof shape: gable (two sloping sides), hip (all sides slope), or flat.
- Choose the roof pitch — steeper pitches increase the effective surface area.
- Enter the length and width of the roof in feet (measured from the ground, including overhangs).
- Adjust the waste factor (default 10%) to account for cuts, ridge caps, and starter rows.
- Optionally enter a price per bundle for a cost estimate.
- Click "Calculate Roofing" to get total area, bundles needed, and material costs.
Formula
Hip Roof Area: L × W × Pitch Multiplier × 1.1
Flat Roof Area: L × W × 1.0
With Waste: Total Area × (1 + Waste% / 100)
Roofing Squares: Total Area / 100
Bundles Needed: Roofing Squares × 3 (standard 3-bundle per square)
A roofing square equals 100 square feet. Standard 3-tab shingles require 3 bundles per square, while architectural shingles may also use 3 bundles per square. One roll of underlayment covers approximately 4 squares (400 sq ft).
Examples
40 ft × 30 ft, medium pitch (1.12x), 10% waste: Area = 40 × 30 × 1.12 × 1.10 = 1,478 sq ft = 14.78 squares = 45 bundles.
50 ft × 35 ft, steep pitch (1.30x), 15% waste: Area = 50 × 35 × 1.30 × 1.1 × 1.15 = 2,860 sq ft = 28.6 squares = 86 bundles.
60 ft × 40 ft, flat, 10% waste, $35/bundle: Area = 60 × 40 × 1.10 = 2,640 sq ft = 26.4 squares = 80 bundles. Cost = 80 × $35 = $2,800.
Frequently Asked Questions
How many bundles of shingles do I need?
Most shingle manufacturers package 3 bundles per roofing square (100 sq ft). To estimate, calculate your roof area, divide by 100 to get squares, then multiply by 3 for bundles. Always add 10–15% extra for waste, ridge caps, and starter strips.
What is a roofing square?
A roofing square is a unit of measurement equal to 100 square feet of roof area. Roofing contractors and suppliers use this unit to quote materials and labor. For example, a 2,500 sq ft roof = 25 roofing squares.
How much waste should I account for?
For simple gable roofs, 10% waste is typical. For hip roofs, dormers, or complex shapes with many valleys and ridges, use 15–20%. Waste comes from cutting shingles to fit edges, ridges, and valleys. It’s better to have a few extra bundles than to run short mid-project.
How to measure roof pitch?
Roof pitch is the rise (vertical) per 12 inches of run (horizontal). Measure from inside the attic: place a level horizontally, measure the vertical rise at 12 inches. A 6/12 pitch rises 6 inches per 12 inches of run. This pitch multiplier accounts for the increased surface area of sloped roofs.