How it works
The calculator adds your waste allowance to the roof area, converts it to squares of 100 sq ft, and multiplies by the bundles per square – or divides by the coverage of one bundle.
Area with waste = Roof area × (1 + Waste ÷ 100)
Squares = Area with waste ÷ 100 sq ft
Bundles = ⌈ Squares × Bundles per square ⌉ or ⌈ Area with waste ÷ Coverage per bundle ⌉
⌈ ⌉ means rounding up to the next whole bundle. Rounding happens only at the end. A metric roof area is converted to squares the same way, using 100 sq ft = 9.290304 m².
Worked example
Inputs
- Roof area
- 1500 sq ft
- Bundle size given as
- Bundles per square
- Bundles per square
- 3
- Waste allowance
- 10 %
Result
- Area incl. waste
- 1,650 sq ft
- Roofing squares
- 16.5 squares
- Bundles
- 50
Common mistakes
- Entering the building footprint instead of the sloped roof area. The roof surface is larger than the ground it covers.
- Assuming every shingle comes 3 bundles to a square. Some products need more bundles per square, and some cover slightly less than 100 sq ft per set of bundles.
- Forgetting waste. Cuts at hips, valleys, rakes and around penetrations use material that cannot be reused.
- Counting ridge and starter courses from field shingles without checking. Many products have dedicated starter and cap shingles sold separately.
Assumptions and limits
- The roof area you enter is the true sloped surface, and the whole area gets the same shingle.
- A square is 100 sq ft. Bundles are rounded up to whole bundles at the end.
- Waste is a single percentage you choose; the calculator does not analyze valleys, hips or cut patterns.
- Starter strip, hip and ridge cap, underlayment, flashing and fasteners are not counted.
Frequently asked questions
How many bundles are in a square?
It depends on the product. The Asphalt Roofing Manufacturers Association’s residential manual says there are typically 3, 4 or 5 bundles per square, and Owens Corning lists 4 bundles per 98.4 sq ft for Duration MAX. Read the wrapper or the data sheet of the shingle you are buying.
What if the bundles don’t cover exactly 100 sq ft?
Choose “Coverage per bundle” and enter the area one bundle covers. For a product rated 4 bundles per 98.4 sq ft, that is 98.4 ÷ 4 = 24.6 sq ft per bundle. Entering “4 bundles per square” instead would come out slightly short.
How much waste should I allow?
It depends on the roof’s shape. A plain gable roof needs the least; hips, valleys, dormers and many penetrations need more. Check the shingle manufacturer’s guidance or ask your roofer, and enter that figure.
Does this include ridge caps and starter strips?
No. Those are usually separate products measured in linear feet along the eaves, rakes, hips and ridges. Check the manufacturer’s coverage figure for each.
Sources
- Residential Asphalt Roofing Manual – Design and Application Methods (2014) — Asphalt Roofing Manufacturers Association (ARMA). "1 square = 100 square feet"; "There are typically 3, 4 or 5 bundles per square." Check the wrapper of your product.
- TruDefinition Duration MAX Shingles – Product Data — Owens Corning. Coverage 98.4 sq ft per 4 bundles: bundles per square differ between products.
Method reviewed November 2, 2026