MEASURE. ESTIMATE. BUILD.
Convert roof rise and run into pitch, angle, and slope factor.
Change any measurement to update your estimate.
A 6-inch rise over 12 inches of run is a 6/12 pitch, about 26.57°, with a slope multiplier of 1.118.
Pitch is rise over a 12-inch run — this view turns your rise/run into an angle and the slope factor that scales roof area above the flat footprint. A 6/12 roof carries about 12% more surface than its footprint.
Order by the square but buy in whole bundles — three bundles cover a square of architectural shingles, and you'll want the extra for ridge caps and starter courses the footprint math doesn't include. Steep and cut-up roofs (valleys, hips, dormers) waste closer to 15% than 10%. If you can't safely measure the roof itself, measure the footprint and let the pitch factor do the work, then add a bundle.
The math behind the tool:
roof area = footprint area × slope factor(pitch)
squares = roof area ÷ 100 × (1 + waste%)Sources: National Roofing Contractors Association (roofing squares and slope terminology).
A roofing square is 100 ft² of roof surface. Divide your total sloped roof area by 100 to get squares; a 2,000 ft² roof is 20 squares.
Pitch increases the sloped area above the flat footprint. A 6/12 pitch has a slope factor of about 1.118, so it needs roughly 12% more material than the footprint alone.