How this calculator works
For one common roof pitch, multiply horizontal footprint by the slope multiplier. A measured sloped area bypasses this correction. Add waste and divide by bundle coverage, rounding up. Purchased bundle count times shingles per bundle gives the number of shingles bought, not the exact pieces installed. Starter strips, ridge caps, valleys, underlayment and flashings are separate unless already included in a product-specific takeoff.
Formula
slope multiplier = sqrt(1 + (rise/run)²); roof area = footprint x multiplier; bundles = ceil(roof area x (1 + waste)/bundle coverage); roofing squares = roof area/9.290304 m2.
Worked example
A 100 m2 horizontal footprint at 9:12 pitch has a 1.25 multiplier, giving 125 m2 roof area. Bundles covering 5 m2 each require 25 bundles before waste.
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Frequently asked questions
Are there always three bundles per square?
No. Many products use about three, but packaging and coverage differ. Enter the exact label coverage for the selected shingle.
Does a flat-pitch result mean shingles are suitable?
No. Zero pitch is allowed for the area arithmetic. Product minimum slope and underlayment requirements must be checked separately.
What if different roof faces have different pitches?
Calculate each section with its own pitch and coverage, then combine the quantities with a sensible cutting allowance.