One roofing square equals 100 square feet of roof surface, not footprint. Bundle count varies by product.
Footprint is not roof surface
A sloped roof covers more surface than the horizontal building footprint. For a simple gable, multiply footprint area by a pitch factor derived from rise over 12 inches of run. Hips, valleys, dormers, additions, and unequal slopes should be measured as separate planes.
Roof measurement is hazardous. Use plans, verified aerial measurements, or a qualified roofer rather than walking a steep, wet, damaged, or unprotected roof.
Squares organize the estimate
Roofing quantities are commonly discussed in squares, with one square representing 100 square feet. Shingles are packaged in bundles, but three bundles per square is only a common convention—not a rule for every product. Read the package coverage for the selected shingle.
Starter strips, ridge caps, underlayment, ice barrier, flashing, ventilation, fasteners, and sheathing repairs are separate lines.
Waste follows roof complexity
Simple gables generally create fewer cuts than roofs with hips, valleys, dormers, and intersecting planes. The waste allowance should reflect the actual cutting plan and product dimensions. Local wind, fire, snow, and ice requirements can also change the complete roof system.
Sources & further reading
References behind this guide
These sources support safety, measurement, or industry context. Product instructions, approved plans, and local requirements control your project.