How it works
Estimate the roof area, roofing squares, and shingle bundles for a gable roof from its footprint and pitch.
Enter the building footprint (length and width), the roof rise, and the run. The calculator scales the flat footprint by the roof-pitch factor to get the sloped roof area, then converts it to roofing squares and shingle bundles.
Formula
Roof area = length × width × √(run² + rise²) ÷ run; squares = roof area ÷ 100; bundles = squares × 3.
L- Building length (ft)
W- Building width (ft)
rise- Roof rise per run (in)
run- Roof run (in)
Examples
- 30 × 20 ft footprint, 6/12 pitchLength 30 · width 20 · rise 6 · run 12Footprint 600 ft² · roof area ≈ 670.82 ft² · 6.71 squares · ≈ 21 bundles
Frequently asked questions
What is a roofing square?
A square is 100 square feet of roof area — the standard unit roofers quote and sell in.
How many bundles per square?
About 3 bundles of standard three-tab shingles cover one square. Heavier architectural shingles can need 4.
What does the pitch affect?
A steeper pitch increases the actual roof surface for the same footprint, so it needs more material.
How to read the result
The roof area is larger than the footprint because the sloped surface covers more area. Squares and bundles are rounded up to whole units for ordering.
Limitations
Assumes a simple gable roof with two identical rectangular slopes. Does not model hips, valleys, dormers, overhangs, waste factor, or complex roof shapes — add 10–15% for waste on real jobs.
Source: Roof pitch factor from the Pythagorean theorem (√(run² + rise²) ÷ run); 1 square = 100 ft²; 3 bundles per square.