Roofing Calculator
Use this roofing calculator to estimate roof area and roofing squares for a simple rectangular roof. Enter footprint length and width, choose roof pitch, and set a waste allowance for a planning estimate.
How to use
Enter the roof footprint length and width, select a pitch such as 6/12, then set waste allowance and calculate. Use bundles per square only when you want an optional asphalt-shingle bundle estimate and know how many bundles cover one square for your product.
How the calculation works
First the calculator finds footprint area (length × width). That area is multiplied by a pitch factor from rise/run geometry to estimate roof surface area. Waste is then applied, and roofing squares equal adjusted roof area ÷ 100. Steeper pitches increase surface area even when the footprint stays the same.
Formula
footprint_ft² = length_ft × width_ft; pitch_multiplier = √(1 + (rise/run)²); roof_area = footprint × pitch_multiplier; adjusted = roof_area × (1 + waste%/100); squares = adjusted ÷ 100; bundles = ceil(squares × bundles_per_square)
Example calculation
A 40 ft × 30 ft footprint at 6/12 pitch: footprint 1,200 ft² × √(1+(6/12)²) = 1,200 × √1.25 ≈ 1,341.64 ft². With 10% waste ≈ 1,475.80 ft² ≈ 14.76 squares.
Assumptions
Geometry
Simple rectangular footprint × pitch multiplier
Material: roofing · Key: geometry
Does not model hips, valleys, dormers, or multi-plane roofs.
Source: Geometric model (not a material constant)
Roofing square (ft² / square)
100 ft²
Material: roofing · Key: square_definition
Industry unit definition for roofing materials.
Source: Common US roofing industry unit (1 square = 100 ft²)
Default bundles per square (bundles / square)
3 bundles per roofing square
Material: roofing · Key: bundle_coverage
A frequent asphalt-shingle planning convention (1 square = 100 ft²). Bundle coverage varies by product — confirm packaging.
Source: Planning default — confirm with your product label or supplier quote. Not a lab or manufacturer certification.
Practical notes
- Measure the building footprint carefully; overhangs may need extra length/width.
- Steeper pitches increase surface area even when the footprint stays the same.
- Waste allowance covers cuts and irregularities before converting area into squares.
- Order starter strips, ridge caps, and underlayment using product guidance — they are not included here.
Limitations
- Not a professional roofing takeoff.
- Hips, valleys, dormers, complex shapes, and local code can change material needs.
- This tool does not calculate sheathing sheet counts, felt or underlayment rolls, or roof tile counts.
- Bundle estimates depend on product coverage assumptions you enter and apply to shingle planning only.
FAQ
- How do I calculate roof area?
- For a simple rectangular roof, multiply footprint length by width, then multiply by the pitch factor √(1 + (rise/run)²). This calculator performs that roof-area estimate from the dimensions and pitch you enter.
- What is a roofing square?
- One roofing square equals 100 square feet of roof surface. After waste is applied, squares equal adjusted roof area ÷ 100.
- What does roof pitch (for example 6/12) mean?
- Pitch is rise over run: inches of rise for every 12 inches of horizontal run. A 6/12 roof rises 6 inches per 12 inches of run. Steeper pitches use larger multipliers and increase roof surface area for the same footprint.
- How does waste allowance work?
- Waste is an extra percentage added to roof area for cuts and irregularities. The calculator applies waste before converting adjusted area into roofing squares.
- Does this estimate roofing materials?
- It provides a planning estimate of roof area and roofing squares, plus an optional shingle-bundle count when you set bundles per square. It does not estimate sheathing, felt or underlayment rolls, ridge or starter pieces, or roof tile counts.
- Can I use this for a hip or complex roof?
- Only as a rough starting point. Hips, valleys, dormers, and cut waste usually need a more detailed takeoff than this simple-roof model.
Related calculators
Results are planning estimates. See the Calculator Disclaimer.