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Roof area calculator
The real sloped roof area from the plan footprint and the pitch — the number shingles, underlayment, and roofing labor are figured on.
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How it’s computed
Sloped area = footprint (sqft) × pitch factor, where the factor = √(rise² + 12²) ÷ 12 — standard roof geometry. A 5/12 pitch ≈ 1.083×, 8/12 ≈ 1.202×, 12/12 ≈ 1.414×.
Decimal-exact and deterministic: identical inputs always return identical results. This is the same math Ask Donnie’s estimating engine runs — not an approximation, and never a language model doing arithmetic.
Common questions
What does pitch "rise per 12" mean?
Inches of vertical rise per 12 inches of horizontal run. A 6/12 roof rises 6" every foot. Read it off the roof plan or measure with a level and a ruler.
Does this include overhangs?
Only if your footprint does. Measure the footprint to the eave edges (not the wall line) to capture the overhang area.
Need the whole estimate, not just this number?
Ask Donnie turns a description or a plan into a full itemized estimate — deterministic math, real cited pricing, an AACE accuracy class. Free to start, watermarked deliverables included.