Formula
Footprint × slope factor = roof surface area. Add the shingle allowance, divide by 100 for squares, then multiply bundles per square.
Roofing Shingle Calculator
Estimate roof surface area, roofing squares, and whole shingle bundles from area or pitch.
How this roofing shingle estimate works
Use a known roof surface area when you have one. The footprint method is a deliberately simple planning shortcut for a uniform pitch and makes its slope factor visible.
Worked example
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.
Before you buy
Confirm the manufacturer’s bundles-per-square coverage, starter strips, ridge caps, valley method, flashing, and local disposal requirements before ordering.
Assumptions
Defaults are starting points. Replace coverage, density, package yield, spacing, and allowance values with the product or plan you are actually using.
Limitations
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.