Estimate roof surface area, roofing squares, and whole shingle bundles from area or pitch.
Use a known roof surface area when you have one. If you only have the building footprint, the second method provides a simple planning shortcut for one uniform pitch and shows the slope factor used.
For footprint mode, multiply the horizontal footprint by the slope factor to estimate roof surface area. Apply the allowance, divide by 100 for roofing squares, and multiply by bundles per square.
A 2,000 sq ft horizontal projection at 6:12 has a slope factor of about 1.118, producing about 2,236 sq ft of roof surface. With 10% allowance and 3 bundles per square, that rounds to 74 bundles.
Confirm the manufacturer's bundles-per-square coverage, starter strips, ridge caps, valley method, flashing, and local disposal requirements before ordering.
Dormers, valleys, hips, multiple pitches, overhangs, shingle profile, bundles per square, flashing, and disposal can change the final material list.
The footprint method does not model dormers, valleys, hips, multiple pitches, or complex roof geometry. Do not use it as instructions to climb or walk on a roof.
Use it when you already have the roof surface measurement. It avoids the extra assumptions in the simple footprint method.
In this calculator, one roofing square is treated as 100 square feet of roof surface.
Shingle coverage depends on the product. Use the manufacturer's package information instead of relying on a generic bundle count.
Short, practical help for the next step in this project.