Roof Pitch and Shingle Material Calculator
Calculate your roof's pitch, slope angle, and estimate the number of shingles (squares) needed for your roofing project.
Formulas Used
Slope Factor = √((rise/12)² + 1)
Slope Angle = arctan(rise / 12) × (180 / π)
Rafter Length = Horizontal Run × Slope Factor
Total Roof Area = Number of Sides × Rafter Length × Ridge Length
Squares Needed = Total Roof Area / 100 × (1 + Waste% / 100)
Bundles Needed = ⌈Squares Needed × 3⌉ (3 bundles per square for standard 3-tab shingles)
Assumptions & References
- Pitch is expressed as rise (inches) per 12 inches of horizontal run — the US standard notation (e.g., 6:12).
- The slope factor converts horizontal (plan) area to actual sloped roof surface area.
- One roofing square = 100 sq ft of roof surface (NRCA standard).
- Standard 3-tab asphalt shingles require 3 bundles per square; architectural/dimensional shingles may require 4 bundles — verify with your supplier.
- A 10% waste factor is typical for simple gable roofs; use 15–20% for complex roofs with hips, valleys, or dormers.
- Pitches below 2:12 are considered low-slope and require modified bitumen or special underlayment per most building codes.
- Rafter length calculated here is the structural rafter span (run to ridge); add overhang length separately.
- Formula reference: Residential Construction Academy: Carpentry, Vogt; NRCA Roofing Manual.