Roofing squares, pitch factors, and shingle bundles
Roofing is purchased by area, but pitch and roof geometry must be translated from a horizontal plan before squares and bundles are rounded.
Core sequenceHorizontal roof-plan area × pitch factor × allowance ÷ 100 = roofing squares.
Measure the horizontal projection
For a simple gable roof, multiply overall eave length by the horizontal width from eave to eave, including overhangs. That footprint represents the plan area beneath both slopes. Multiplying by the pitch factor converts it to approximate sloped surface area.
Do not use building interior dimensions when the roof extends beyond the walls.
Pitch changes surface area
A 6:12 roof rises 6 inches for every 12 inches of horizontal run. Its slope factor is about 1.118, so 1,000 square feet of horizontal roof plan becomes about 1,118 square feet of sloped roof before allowance.
For complex roofs, measure each plane or obtain dimensions from reliable plans instead of applying one factor to the entire building.
Squares and bundles are different rounds
One roofing square is 100 square feet. Shingles are sold in bundles whose stated coverage determines the number required per square. Apply allowance to area first, then round to full bundles using the current product packaging.
- Starter shingles may use linear-foot coverage.
- Ridge and hip caps are separate from field shingles.
- Underlayment and membrane follow their own overlap and coverage rules.
Safety and scope remain outside the calculator
Roof access, fall protection, deck condition, ventilation, flashing, ice barriers, fastening, wind rating, fire classification, tear-off, and local requirements cannot be chosen from area alone. Verify the complete system with current manufacturer instructions and qualified roofing guidance.