How to Calculate Shingles
Roofing materials are measured in "squares" — one square covers 100 square feet of roof area. But roof area isn't the same as floor area. A pitched roof covers more surface area than the flat footprint of the building below it. A 6/12 pitch (one of the most common residential pitches) adds about 12% to the flat area. A 12/12 pitch (45 degrees) adds 41%. The pitch multiplier is built into this calculator.
Squares = Roof area ÷ 100
Bundles = Squares × Bundles per square (3 for standard shingles)
Pitch Multiplier Reference
- 4/12 pitch — multiplier 1.054 (adds 5.4% to flat area)
- 6/12 pitch — multiplier 1.118 (adds 11.8%)
- 8/12 pitch — multiplier 1.202 (adds 20.2%)
- 10/12 pitch — multiplier 1.302 (adds 30.2%)
- 12/12 pitch — multiplier 1.414 (adds 41.4%)
The pitch multiplier is derived from the Pythagorean theorem: multiply the flat area by √(1 + (rise/12)²). The calculator handles this math automatically. If you don't know your roof pitch, measure the rise and run with a level and tape measure in the attic, or check your original building plans.
Shingle Types and Bundle Counts
3-Tab shingles are the most economical option — flat appearance, 20–25 year warranty, 3 bundles per square. Architectural (dimensional) shingles are the current standard for most homes — layered appearance, 30–50 year warranty, also 3 bundles per square but heavier. Designer and premium shingles mimic slate or wood shake and typically require 4 bundles per square. Wood shakes are thicker and require 5 bundles per square.
Most major manufacturers — GAF, CertainTeed, and Owens Corning — publish detailed specification sheets with exact coverage per bundle for each product line. When in doubt, check the product data sheet for your specific shingle.