FitAndFillRoofing Calculator: Squares and Bundles of Shingles
Estimate the roof area, roofing squares and bundles of shingles from the roof footprint and its pitch, with an allowance for cuts and waste.
How the calculation works
A sloped roof has more surface than the floor plan under it. The calculator multiplies the footprint by a pitch factor, then converts to roofing squares (100 sq ft each) and bundles.
pitch factor = √(1 + (rise ÷ 12)²) roof area (sq ft) = length × width × pitch factor + extra area squares = roof area ÷ 100 bundles = squares × (1 + extra) × bundles per square, rounded up | Pitch | Factor | Pitch | Factor |
|---|---|---|---|
| 3/12 | 1.031 | 6/12 | 1.118 |
| 4/12 | 1.054 | 8/12 | 1.202 |
| 5/12 | 1.083 | 9/12 | 1.25 |
| 6/12 | 1.118 | 10/12 | 1.302 |
| 7/12 | 1.158 | 12/12 | 1.414 |
Worked example
A 40 ft × 30 ft roof footprint (1,200 sq ft) with a 6/12 pitch has a factor of 1.118, so the roof surface is 1,342 sq ft, or 13.42 squares.
Adding 10 % for cuts and waste gives 14.76 squares. At 3 bundles per square that is 44.3, so buy 45 bundles.
Assumptions and limits
- Every slope of the roof has the same pitch. For roofs with different pitches, calculate each part separately and add it as extra area.
- The length and width are the roof footprint seen from above, including overhangs.
- One roofing square is 100 sq ft. Bundles per square comes from the shingle package; the list offers 3, 4 and 5.
- The extra for cuts and waste is an allowance you choose; roofs with valleys, hips and dormers usually need more. Ask your roofer or the manufacturer.
- Starter strips, ridge caps, underlayment, flashing and nails are not included.
- This is a material estimate, not a substitute for a professional measurement. Do not climb a steep, wet or damaged roof.
Frequently asked questions
What is a roofing square?
It is the trade unit for roof area: one square covers 100 sq ft. The shingle package tells you how many bundles cover a square; many packages say 3, but check yours.
How do I find the pitch?
Pitch is written as "6/12": 6 inches of rise for every 12 inches of horizontal run. You can read it from the building plans, measure it from the attic along a rafter, or ask your roofer. Do not climb a steep, wet or damaged roof to measure it.
How much extra should I buy?
The default is 10 %, a starting point for a simple roof. Roofs with valleys, hips, dormers or many cuts usually need more, so ask your roofer or the shingle manufacturer. This tool does not include starter strips, ridge caps, underlayment, flashing or nails.
Does it work for hip and gable roofs?
Yes, when every slope has the same pitch. If parts of the roof have different pitches, calculate each part separately and enter the result of the others in "Extra area".
Is this a substitute for a roofer's quote?
No. It is a planning estimate for materials. Roofing is dangerous work, and a professional measurement and quote are the safer basis for ordering.
Sources
- Trade definition: one roofing square = 100 square feet of roof
- Geometry: the sloped surface is √(1 + (rise ÷ 12)²) times its horizontal projection (Pythagorean theorem)
- Bundles per square: entered by the user from the package of the shingles they plan to buy (the tool does not assume a brand)
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