How this calculator works
Estimate roof surface area from a rectangular footprint and roof pitch, then convert area into roofing squares and approximate bundles.
Formula
Sloped area = footprint including overhang × pitch factor, where pitch factor = √(1 + (rise/12)²). Squares = area ÷ 100; bundles = squares × bundles per square.
Sloped area = footprint including overhang × pitch factor, where pitch factor = √(1 + (rise/12)²). Squares = area ÷ 100; bundles = squares × bundles per square.
Example
A 6:12 roof has a pitch factor of about 1.118, so its surface area is larger than the building footprint.
Reliability check
Use this model only for a rectangular gable footprint. For hips, valleys, dormers or intersecting roofs, measure each plane and calculate starter, ridge and cap products separately.
How to get a better estimate
- Hip roofs, valleys, dormers and multiple sections need separate measurements.
- Always verify bundle coverage for the selected shingle.
- Roof work is hazardous; measurements can often be taken from plans or professional reports.
What the result means
This model uses a simple rectangular building footprint and pitch factor. Complex roofs should be measured by plane and include hips, valleys, ridges, starters and flashing.