How to Calculate Roofing Shingles
From roof area to bundles and squares, with waste and starter courses
Start with roof area, not footprint
Shingle calculations start from the true sloped roof area (footprint × slope factor), not the building's flat footprint. Using the footprint alone under-orders material for anything but a flat roof.
Roofing 'squares'
Roofing is priced and ordered in squares — one square covers 100 square feet of roof. Divide the roof area by 100 to get the number of squares. Standard three-tab or architectural shingles typically come 3 bundles to a square, though bundle counts vary by product and manufacturer.
Add waste for cuts and hips/valleys
A simple gable roof typically needs a smaller waste allowance (around 10%) than a roof with multiple hips, valleys, and dormers, where cutting waste can run 15-20% or higher. This is on top of the base square count from the roof area.
Starter strips and ridge caps are separate
Starter courses along the eaves and ridge/hip cap shingles are ordered separately from the field coverage — they're linear-footage items (based on eave and ridge/hip length), not part of the per-square field coverage calculation.
Worked Example
A roof area of 1,342 ft², simple gable, 10% waste, 3 bundles per square.
Squares (exact): 1,342 ÷ 100 = 13.42 squares
With 10% waste: 13.42 × 1.10 ≈ 14.76 squares
Bundles: 14.76 × 3 ≈ 45 bundles (round up)
Assumptions & Limitations
- Bundle-per-square counts vary by manufacturer and shingle type — confirm against the specific product's packaging.