Roofing Calculator
Estimate roofing squares, bundles, underlayment and cost from your footprint and roof pitch.
Your details
Rise in inches per 12 inches of horizontal run. This is what turns footprint into actual roof area.
Ten percent for a simple gable; fifteen to twenty for hips, valleys and dormers.
Cost
A square is 100 square feet. Architectural shingles typically run $100 to $180 per square in materials.
This calculator runs entirely on your device. Nothing you enter is uploaded, stored, or sold. How this works
Roofing squares needed
16.8
1,683 sq ft including 12% waste
Includes your inputs, the full breakdown, and every row of the table.
Actual roof area
1,503 sq ft
Shingle bundles
51
Pitch multiplier
1.1180
Estimated total cost
$7,055
- Footprint with overhang
- 1,344 sq ft
- Pitch multiplier at 6/12
- × 1.1180
- Sloped roof area
- 1,503 sq ft
- Waste at 12%
- + 180 sq ft
- Squares to buy
- 17 squares
- Materials
- $2,040
- Labour
- $4,250
- Tear-off, 1 layer
- $765
- Estimated total
- $7,055
| Item | Quantity | Basis | Cost |
|---|---|---|---|
| Shingle bundles | 51 | 3 per square | $2,040 |
| Ridge cap bundles | 3 | ~20 lin ft each | — |
| Underlayment rolls | 5 | 400 sq ft each | — |
| Drip edge (10 ft lengths) | 15 | 148 lin ft | — |
| Roofing nails (lb) | 43 | ~2.5 lb per square | — |
What this means
- A 6/12 pitch is 26.6 degrees, which makes the actual roof surface 11.8% larger than the footprint below it. Ordering from footprint alone is the classic way to come up short.
- This pitch is walkable, so labour should be near standard rates.
- Squares are sold whole and shingles come three bundles to the square. Order the full square — running out mid-job risks a dye-lot mismatch that will be visible from the street for the life of the roof.
How the roofing calculation works
Roofing is priced in squares, where one square is one hundred square feet. The number that trips people up is not the arithmetic but the pitch: a roof is a sloped surface sitting above a flat footprint, and the steeper it is, the more material it takes to cover the same ground. A common six-in-twelve pitch adds about twelve percent to the area, and a twelve-in-twelve adds over forty percent. Estimating from the footprint alone guarantees a short order.
The pitch multiplier is straightforward trigonometry — the hypotenuse of a triangle with a twelve-inch run and a rise equal to the pitch, divided by twelve. What it does not capture is complexity. Every valley, hip, dormer and penetration means cuts, and every cut generates offcuts you cannot use elsewhere. That is what the waste allowance is for, and it is why a simple gable roof gets ten percent while a cut-up roof with multiple dormers needs closer to twenty.
Tear-off is the cost most often left out of a mental estimate and it is rarely trivial. Removing existing layers, disposing of them, and inspecting the decking underneath adds meaningfully to the job, and a second layer roughly doubles that portion. Building codes in most jurisdictions cap the number of layers at two, so if there are already two on the roof, a full tear-off is not optional.
Frequently asked questions
How many bundles of shingles do I need?
Three bundles cover one square, or one hundred square feet, for standard three-tab and most architectural shingles. Calculate your sloped roof area, add waste, divide by one hundred, and multiply by three — then round up to whole bundles.
Why does roof pitch change how much material I need?
Because a sloped surface is larger than the flat area beneath it. A 6/12 pitch roof has about twelve percent more surface than its footprint, and a 12/12 has over forty percent more. Ordering from the building footprint without applying the pitch multiplier is the most common estimating error.
How much waste should I allow for roofing?
Ten percent for a straightforward gable roof with few penetrations, and fifteen to twenty percent once you have hips, valleys or dormers. Complex roofs generate offcuts at every cut line, and those pieces usually cannot be used elsewhere.
Do I have to tear off the old roof?
Not always, but often. Most codes allow a maximum of two layers, so a second layer can sometimes be laid over the first. Tearing off is still generally better because it lets you inspect the decking, and a roof-over adds weight while shortening the life of the new shingles.
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Disclaimer. This calculator is provided for general information and educational purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Results are estimates based on the inputs you provide and the assumptions described above. Confirm any figure with a qualified professional before acting on it.