Roofing Material Calculator
1,341.64 sq ft of roof
13.42 squares (roof area 1341.64 sf = footprint × 1.12 slope factor); 1475.8 sf with 10% waste.
45 bundles (OC-class 32.8 sf/bundle, whole-bundle round-up).
- Sloped area = footprint × √(1+(rise/12)²) = 1200 × 1.12. Pure geometry: include eave/rake overhangs in your footprint or this understates.
- Waste: 10% for simple gable (JLC convention). Waste is a range by design; cut-up roofs can exceed 15%.
- Footprint estimation fails on complex plans (dormers, turrets, intersecting gables); measure each roof plane there instead.
- A 4/12-vs-8/12 pitch mistake is a 14% area error: verify pitch, don't guess it.
- Bundles: whole-bundle round-up at 32.8 sf/bundle (product-specific, OC Oakridge TDS). 3 bundles/square mainstream.
Why This One Is Different
Price your reroof off shingle bundles alone and you'll come up short at the register, because “roofing material” actually spans four or five separate SKUs, and most calculators only price the one that's easiest: field shingles. Your 24-square roof needs roughly 72 bundles of architectural shingles at 3 bundles/square, and that part is simple arithmetic. What usually gets left off the list is ridge cap (sold by the linear foot, in bundles that don't map cleanly to squares), starter strip (also linear feet, along eaves and rakes), and underlayment (sold in rated squares that shrink once side and end laps are subtracted). Forgetting any one of those is the single most common gap between a quick estimate and the real material list you need on a tear-off job.
Where the Numbers Come From
- Mainstream architectural shingles run 3 bundles/square (~32.8-33.3 sf/bundle); designer/heavyweight lines break that rule at 4-5 bundles/square. Verify per product. Source: GAF Timberline HDZ spec sheet (3 bundles/square, primary source read); OC Oakridge TDS (32.8 sf/bundle)
- Ridge cap and starter strip are separate purchases sold by the linear foot (commonly ~25 lin ft/bundle ridge, ~120 lin ft/bundle starter), not derived from the square count. Source: roofing purchase-unit convention (retailer product listings; GAF spec sheets)
- Underlayment coverage is rated net of side and end laps: a “10-square” roll does not cover 10 squares of roof once laps are subtracted. Source: GAF FeltBuster data sheet (10-square roll, coverage excludes laps)
- Waste percentage applies to field shingles only; accessory items (ridge, starter, underlayment) are counted from linear/area takeoffs, not multiplied by a waste factor. Source: worked example, closed-form geometry
More Questions
Does the waste factor apply to ridge cap and starter strip too?
No, waste percentages are a field-shingle convention. Ridge and starter are taken off from linear footage (ridge/hip length, eave+rake length) and rounded up to whole bundles instead.
Related Calculators
Formulas, waste factors, and cost models on this page follow the sourced conventions on our methodology page. Estimates only; verify with your supplier and local code.