The math behind the multiplier
Roof surface grows with slope. The pitch multiplier is √(1 + (rise ÷ 12)²). A 4/12 roof is about 5.4% larger than its footprint; an 8/12 roof is about 20.2% larger; a 12/12 roof about 41.4%.
Flat and low-slope roofs
Many New Mexico homes have flat roofs behind parapets. Pick 2/12 or lower for a close approximation, but remember that parapet walls, cants, crickets and flashing are measured and priced separately from the field of the roof. Those are the items most often missing from a carrier’s flat-roof scope.
Checking an estimate
- Compare total squares and the waste percentage with this result; a gap over 5–10% is worth asking about.
- Look for steep charges (commonly 7/12 and up) and two-story charges.
- Confirm drip edge, starter, ridge cap, valley metal and flashing are listed.
Questions about this estimator
What is a roofing square?
One square is 100 square feet of roof surface, measured on the slope rather than on the ground.
Is this as good as an aerial report?
No. Roofs with several planes, dormers or valleys need to be measured plane by plane. Use this as a sanity check.
Is anything I type saved or sent?
No. The tool runs entirely in your browser. Close the page and the numbers are gone.