Roofing Calculator
Roof area in roofing squares, from a footprint and pitch or from an area you have already measured. Bundle counts appear only when you tell us what one bundle covers.
Switching units keeps your measurements. Nothing is reset.
What do you know?
The plan area of the building, measured on the ground.
The footprint route assumes a simple gable roof. Hips, valleys, dormers and complex shapes need the roof area measured directly.
Your shingles
Optional, and printed on the wrapper. Without it the answer stays in squares.
Waste allowance
10% covers cuts at hips, valleys, ridges and starter courses.
Offcuts, breakages, pattern matching and the occasional damaged piece all mean you use more material than the bare area. Keeping a few spare pieces for future repairs is also normal.
This is a planning allowance, not a rule. Adjust it for your layout, your material and your own tolerance for a second trip to the store.
Estimated cost
Cost uses the price you enter. This product never shows invented market prices.
Your result appears here
Enter the roof area, or the footprint and pitch, to get started.
How to use this calculator
- 1
If you know the roof area, enter it directly. That is the sloped surface, not the ground the building sits on.
- 2
Otherwise, enter the building footprint and the pitch, and the slope factor is applied for you. This route assumes a simple gable.
- 3
Adjust the waste allowance for the complexity of the roof: hips, valleys and dormers all cut more material.
- 4
Add the coverage from your shingle wrapper if you want a bundle count rather than squares.
A worked example
A 1,200 ft² footprint at a 6 in 12 pitch, with 10% waste and bundles covering 33.3 ft²:
Roof area
1,341.6 ft²1,341.6 ft²
Add the waste allowance
1,341.6 ft² × 1.11,475.8 ft²
Divide by the coverage of one package
1,475.8 ft² ÷ 33.3 ft²44.32
Round up to whole packages
round up 44.3245
Coverage you are buying
45 × 33.3 ft²1,498.5 ft²
You will need
45 bundles
This example is produced by running the calculator above, so it always matches what the tool does.
The formula
Roof area is the footprint multiplied by the slope factor, which is the rafter length over the run. Roofing squares are the roof area divided by 100 square feet, since a square is defined as 100 square feet. The waste allowance is applied to the area, and bundles are that area divided by the coverage on the wrapper, rounded up.
Estimating a roof
Three bundles to a square is not a rule
It is true for many common three-tab shingles and false for plenty of architectural and premium products. This calculator asks for the coverage on your wrapper rather than assuming it, which is why a bundle count only appears once you supply that figure.
The footprint route is for simple gables only
A hip roof, valleys, dormers or an L-shaped plan all add surface that a footprint and a single pitch cannot describe. For those, measure the roof planes directly and enter the area.
Waste rises sharply with complexity
A plain gable wastes little. Every valley, hip and dormer means cut shingles along a diagonal, and starter and ridge courses consume material that never covers a full square.
Common questions
- How many squares is my roof?
- Divide the roof area in square feet by 100. A 1,200 square foot footprint at a 6 in 12 pitch has a roof area of about 1,342 square feet, which is roughly 13.4 squares before waste.
- How many bundles of shingles do I need?
- Divide the roof area, including waste, by the coverage printed on the bundle wrapper, then round up. The coverage differs between shingle types, so this calculator asks for it rather than assuming three bundles to a square.
- Can I use this for a hip roof?
- Not from the footprint. Measure the actual roof planes and enter the total area instead. The footprint route here is honest about being for a simple gable rather than quietly producing a wrong number.