Roof Area Calculator
Your roof is larger than your building footprint because of the slope. Enter your building dimensions, roof pitch, and overhang to calculate the actual roof surface area. Results include roofing squares (1 square = 100 sq ft) so you can order shingles, underlayment, and other materials accurately.
How the Calculation Works
Roof Area = Footprint Area x Pitch Multiplier
The footprint area includes the overhang on all sides. The pitch multiplier converts flat area to sloped area based on how steep the roof is.
Pitch Multiplier Table
| Pitch | Multiplier | Angle | Description |
|---|---|---|---|
| 3/12 | 1.031 | 14.0 degrees | Low slope, minimum for shingles |
| 4/12 | 1.054 | 18.4 degrees | Standard residential |
| 5/12 | 1.083 | 22.6 degrees | Common residential |
| 6/12 | 1.118 | 26.6 degrees | Moderate slope |
| 7/12 | 1.158 | 30.3 degrees | Steeper residential |
| 8/12 | 1.202 | 33.7 degrees | Steep, walkable with care |
| 9/12 | 1.250 | 36.9 degrees | Steep, roof jacks recommended |
| 10/12 | 1.302 | 39.8 degrees | Very steep |
| 12/12 | 1.414 | 45.0 degrees | Maximum standard pitch |
The multiplier is calculated as sqrt(1 + (pitch/12)^2). A steeper roof has more surface area covering the same footprint.
Understanding Roofing Squares
Roofing materials are sold in "squares." One square covers 100 square feet. A bundle of 3-tab shingles covers about 33 sq ft, so you need 3 bundles per square. Architectural shingles vary by manufacturer, but most require 3-4 bundles per square.
Waste Factor Guidelines
- Simple gable roof: 5-10% waste
- Standard hip roof: 10-15% waste
- Complex roof with valleys: 15-20% waste
- Irregular shapes and dormers: 15-25% waste