Contractor field notes
Estimate sloped roof area, shingle bundles, and cost
A horizontal roof footprint understates the surface area of a pitched roof. This calculator adjusts one entered footprint for a uniform rise-per-12 pitch, adds waste for bundle quantity, and prices materials, tear-off, and labor.
Roof pitch and bundle formulas
Sloped area = horizontal footprint × √(1 + (pitch rise ÷ 12)²). Adjusted area = sloped area × (1 + waste percentage ÷ 100). Bundles = adjusted area ÷ bundle coverage, rounded up.
Worked example
For a 1,000 sq ft footprint with 6-in-12 pitch, sloped area is 1,000 × √1.25 = 1,118.03 sq ft. With 10% waste, allow 1,229.84 sq ft. At 33.33 sq ft per bundle, buy 37 bundles. At $40 per bundle, $1 tear-off and $2 labor per sloped sq ft, cost is $1,480 + $1,118.03 + $2,236.07 = $4,834.10 (rounded).
Common estimating pitfalls
- Mixed pitches and complex roof shapes require separate measurements.
- Waste affects bundle quantity; tear-off and labor use sloped area before waste.
Frequently asked questions
What does a 6-in-12 roof pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run. Enter 6 as the rise-per-12 value.
What is a roofing square?
A roofing square is 100 square feet of roof area. Bundle coverage depends on the selected product and should be checked with the manufacturer.
Are flashing, underlayment, and disposal included?
Not as separate automatic line items. Add project-specific costs beyond the entered bundles, tear-off rate, and labor rate.