Roof area & materials calculator

Calculate roof area, shingle bundles, and sheathing sheets from building dimensions and pitch.

Roof type

Building length

Building width

Pitch (rise/12)

/12

26.6° slope

Overhang

All sides

Gable roof

Roof area (slope)

1221 sqft

12.2 squares

Slope factor

1.1180x

6/12 pitch

Shingle bundles

37 + 10% waste

Sheathing (4x8)

43 sheets

39 + 10% waste

Ridge cap bundles

~33 lin ft each

Effective footprint

42.0' x 26.0'

Including overhang

How to Estimate Roofing Materials

Roofing materials are sold in squares — one square covers 100 square feet. Shingles come 3 bundles per square. To estimate, calculate the total sloped roof area and divide by 100.

The slope factor converts flat (plan-view) area to actual sloped area. A 6/12 pitch has a slope factor of 1.118 — meaning the actual roof surface is about 12% larger than the building footprint.

Waste Factors

Gable roofs: 10% waste is typical — mostly from starter course and ridge cuts
Hip roofs: 15% waste due to angled cuts along hip lines and more starter courses
Complex roofs with valleys, dormers, or multiple planes may need 20%+ waste factor

These calculators are provided for estimation and educational purposes only.