Roofing Calculator
Enter your roof footprint dimensions and pitch to instantly calculate roof area in square feet, roofing squares, and shingle bundles needed — including waste factor.
Roof Dimensions
How this calculation works
Step 1 — Pitch factor
Pitch factor = √(1 + (rise ÷ 12)²) Converts your horizontal footprint to actual sloped surface length using the Pythagorean theorem. A 4/12 pitch gives √(1 + (4÷12)²) = √(1.1111) ≈ 1.0541.
Step 2 — Sloped roof area
Sloped area = Length × Width × Pitch factor Multiplies the footprint area by the pitch factor to get true surface area in square feet.
Step 3 — Roofing squares
Squares = Sloped area ÷ 100 One roofing square = 100 sq ft. The standard ordering unit used by contractors and suppliers.
Step 4 — Shingle bundles
Bundles = ⌈ Squares × 3 × Waste factor ⌉ Standard 3-tab and architectural asphalt shingles: 3 bundles cover 1 square (≈33.3 sq ft per bundle). Source: IKO Industries, verified June 2026. Premium or luxury shingles may require 4–5 bundles per square — check your product’s data sheet.
Pitch Factor Reference Table
Shows the area multiplier for each standard roof pitch. Your selected pitch is highlighted. See also: Roof Pitch Calculator — convert pitch to degrees or percentage slope.
| Pitch | Rise | Angle | Pitch Factor | Area vs Flat |
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Related tools: Roofing Squares Calculator · Shingle Calculator · Rafter Length Calculator
Related Roofing Calculators
- Roof Pitch Calculator — convert rise/run to degrees, percentage slope, or pitch ratio
- Roofing Squares Calculator — fast area-to-squares conversion with pitch adjustment
- Shingle Calculator — bundles, nails, and underlayment rolls in one tool
- Roof Area Calculator — compute total surface area for any roof shape
- Rafter Length Calculator — find common rafter length from span and pitch
Frequently Asked Questions
A roofing square is 100 square feet of roof surface area. Contractors and material suppliers use this unit to simplify ordering — for example, a 2,000 sq ft roof is 20 squares.
For standard 3-tab and architectural asphalt shingles, 3 bundles cover one roofing square (100 sq ft). Premium or luxury shingles may require 4–5 bundles per square — always check the product's technical data sheet before ordering.
Use 10% for a simple gable roof with no valleys. Use 15% (the default) for a typical suburban home. Use 20–25% for complex roofs with multiple hips, valleys, dormers, or tight angles where there is more off-cut waste.
Yes. A steeper roof has more actual surface area than the floor footprint suggests. A 6/12 pitch roof has about 12% more surface area than a flat roof of the same footprint; a 12/12 pitch has about 41% more. This calculator applies the correct pitch factor automatically.
The pitch factor (also called the roof slope multiplier) converts horizontal footprint area to true sloped surface area. It equals √(1 + (rise÷12)²). For a 4/12 pitch the factor is approximately 1.054, meaning the actual roof surface is about 5.4% larger than the floor footprint.