Roofing Calculator
Estimate roofing squares, shingles, underlayment, and total material cost for any roof shape. Supports gable, hip, gambrel, and flat roofs with waste factor included.
Rise over run (e.g., 6/12 = 6 inches rise per 12 inches run)
Distance the roof extends beyond the walls
Waste Factor
Standard: 10% | Complex roofs: 15-20% | Simple gable: 5-10%
Material Costs
Default costs based on typical asphalt shingle roofing materials. Click "Edit Costs" to customize prices for your area.
Roofing Estimate
Roofing Tips
- Always add 10-15% extra for cuts and waste
- 1 roofing square = 100 sq ft = 3 bundles
- Ice & water shield at eaves and valleys
- Check local codes for ventilation requirements
How to Calculate Roofing Materials
Calculating roofing materials accurately is crucial for any roofing project. Whether you're installing asphalt shingles, metal roofing, or tile, knowing how many roofing squares you need helps you budget properly and order the right amount of materials.
What is a Roofing Square?
A roofing square is the standard unit of measurement in the roofing industry. One roofing square equals 100 square feet of roof area. When contractors quote roofing jobs, they typically price by the square.
Calculating Roof Area by Type
Gable Roof
Two rectangular planes meeting at a ridge.
Area = Length × Width × Slope FactorSlope Factor = √(1 + pitch²)
Hip Roof
Slopes on all four sides meeting at a ridge.
Area = Base × Slope Factor × 1.055% extra for hip ridges
Gambrel Roof
Two different slopes on each side (barn style).
Area = Base × (Slope₁ + Slope₂) / 2Lower slope steeper than upper slope
Flat/Low Slope
Minimal pitch, requires different materials.
Area ≈ Base × 1.02 to 1.05Usually 2-5% over footprint
Slope Factor Table (Common Pitches)
| Pitch | Angle | Slope Factor |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45.0° | 1.414 |
Additional Materials
- • Underlayment: 1 square per roofing square
- • Ice & Water Shield: 15% of total (eaves + valleys)
- • Drip Edge: Perimeter of roof (linear feet)
- • Ridge Vent: Length of ridge (linear feet)
- • Flashing: Valleys, chimneys, penetrations
Waste Factors
- • Simple Gable: 5-10% waste
- • Hip Roof: 10-15% waste
- • Complex/Cut-up: 15-20% waste
- • Dormers/Valleys: Add 5% extra
- • Starter Strip: Perimeter × 1.5
How It Works
Select Roof Type
Choose from gable, hip, gambrel, or flat roof. Each type has specific calculation formulas.
Enter Dimensions
Input length, width, pitch, and overhang. Add multiple sections for complex roofs.
Get Materials List
Receive roofing squares, bundles, underlayment, and total cost with waste factor.
Don't know your roof's pitch? Calculate your roof pitch first for an accurate material estimate.
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