Roofing Calculator
Calculate the number of roofing squares, bundles of shingles and underlayment a roof needs.
Last updated · View algorithm, constants and default inputs (JSON)
About this calculator
A roofing square is 100 sq ft. The estimate assumes 3 shingle bundles per square and 1 underlayment roll per 10 squares; actual package coverage varies. Cost uses fractional squares after waste, so it may differ from a supplier quote based on whole bundles or squares. Labor and other materials are excluded.
Worked example
calculated with the default values below
Roof footprint area 1,500 sq ft · Roof pitch (rise per 12) 6 · Waste allowance 10 % · Price per square 130 $ Roof surface area 1,845 sq ft · Roofing squares 18.45 squares · Bundles of shingles 56 · Underlayment rolls (10 sq each) 2 · Estimated material cost 2,398.18 $
General background references
Disclaimer
These calculators provide planning estimates only. Building codes, wiring regulations and safety requirements differ by country and change over time, and nothing here replaces a licensed professional or a permit. For structural, electrical or gas work, follow local code and have the installation inspected.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
A = F × √(144 + P²) ÷ 12 × (1 + w ÷ 100); B = ceil(3A ÷ 100)
- F
- Footprint area (sq ft)
- P
- Pitch (per 12 in)
- w
- Waste allowance (%)
- A
- Sloped roof area (sq ft)
- B
- Shingle bundles
A roofing square is 100 sq ft. This calculator assumes 3 shingle bundles per square and 1 underlayment roll per 10 squares; actual package coverage varies. Cost uses fractional squares after waste and is not a supplier-ready rounded purchase quote.
Frequently asked questions
How are roof material quantities and cost estimated?
The surface estimate applies the pitch multiplier and the selected waste allowance. Bundle counts assume three bundles per 100 sq ft; rolls assume 1,000 sq ft each. In the 1,500 sq ft footprint example at 6/12 pitch and 10% waste, this gives about 1,845 sq ft, 56 bundles and 19 rolls. Cost uses 18.45 fractional squares at the entered price, so it may differ from a quote using whole-square pricing.