Roofing Calculator
This roofing calculator turns a house footprint and roof pitch into roof area, roofing squares and shingle bundles. Roof area = footprint × pitch factor, where the pitch factor is √(1 + (rise ÷ 12)²); divide by 100 for squares, add waste, and multiply by bundles per square (usually 3).
At a glance
- What it does: roof area, squares, bundles, pitch factor and angle, and shingle cost if you enter a bundle price.
- What you need: the length and width at the eaves (or the footprint plus overhang) and the pitch.
- What it costs: nothing. It runs in your browser, and nothing you type is sent or stored.
Roof square footage calculator
Measure the outside of the house at the eaves, or the footprint plus the overhang on every side. Choose the pitch and the calculator does the rest.
Shingles only. Order starter strip, ridge cap, underlayment, drip edge and nails separately, and check every number against the manufacturer's coverage on the bundle.
How to calculate roof squares
A roof is longer than the floor under it because it slopes. The pitch factor is how much longer. It comes straight from the right triangle that the rise and run make:
pitch factor = √(1 + (rise ÷ 12)²)
roof area = footprint area × pitch factor
squares = roof area ÷ 100
bundles = squares × (1 + waste %) × bundles per square, rounded up
Worked example
A house measures 40 ft by 30 ft at the eaves, with a 6/12 roof and 10% waste.
- Footprint: 40 × 30 = 1,200 sq ft.
- Pitch factor for 6/12: √(1 + 0.5²) = √1.25 = 1.1180.
- Roof area: 1,200 × 1.1180 = 1,341.6 sq ft.
- Squares: 1,341.6 ÷ 100 = 13.42.
- With 10% waste: 13.42 × 1.10 = 14.76 squares.
- Bundles: 14.76 × 3 = 44.3, so order 45 bundles.
Those are the numbers the calculator above opens with, so you can check it.
Why the footprint method works for hip roofs too
If every face of the roof has the same pitch, the sloped area is always the flat footprint times the same pitch factor, whether the roof is a gable, a hip or a mix. That is why you can measure from the ground. If parts of the roof have different pitches, work out each part on its own and add them up.
Roof pitch multiplier table
Multiply the footprint by the factor for your pitch. The last column shows the roof area over a 1,000 sq ft footprint.
| Pitch | Factor | Angle | On 1,000 sq ft |
|---|---|---|---|
| 0/12 | 1.0000 | 0.0° | 1,000 sq ft |
| 1/12 | 1.0035 | 4.8° | 1,003 sq ft |
| 2/12 | 1.0138 | 9.5° | 1,014 sq ft |
| 3/12 | 1.0308 | 14.0° | 1,031 sq ft |
| 4/12 | 1.0541 | 18.4° | 1,054 sq ft |
| 5/12 | 1.0833 | 22.6° | 1,083 sq ft |
| 6/12 | 1.1180 | 26.6° | 1,118 sq ft |
| 7/12 | 1.1577 | 30.3° | 1,158 sq ft |
| 8/12 | 1.2019 | 33.7° | 1,202 sq ft |
| 9/12 | 1.2500 | 36.9° | 1,250 sq ft |
| 10/12 | 1.3017 | 39.8° | 1,302 sq ft |
| 11/12 | 1.3566 | 42.5° | 1,357 sq ft |
| 12/12 | 1.4142 | 45.0° | 1,414 sq ft |
| 14/12 | 1.5366 | 49.4° | 1,537 sq ft |
| 16/12 | 1.6667 | 53.1° | 1,667 sq ft |
| 18/12 | 1.8028 | 56.3° | 1,803 sq ft |
| 24/12 | 2.2361 | 63.4° | 2,236 sq ft |
How to find your roof pitch
Hold a level flat against the underside of a rafter or on the roof surface, mark 12 inches along it, and measure straight up (or down) from that mark to the roof. That many inches is the rise, so 6 inches means a 6/12 pitch. A phone angle app works too: 26.6° is 6/12, and the table above lists the rest.
How many bundles of shingles per square?
A roofing square is 100 sq ft of roof. Most asphalt shingles, 3-tab and many architectural lines, come three bundles to the square, about 33.3 sq ft per bundle; Owens Corning lists its Supreme 3-tab at 33.3 sq ft per bundle, for example. Some heavier designer shingles need four or five bundles per square, so read the coverage on the wrapper and set it in the calculator.
- Waste: you lose shingle at every cut, valley and hip. A plain gable wastes little; a cut-up roof wastes more. Set the percentage to match the roof.
- Starter and ridge: these are bought by the linear foot of eave, rake, hip and ridge, not by area.
- Tear-off: if you are removing layers, price the disposal by the square too.
Turning a roofing estimate into a quote
Materials are only part of the price. Add labour, disposal, permits and your margin. The margin calculator turns your cost into a price at the margin you want, and job costing shows what each roof made after the work is done.
When the customer says yes, send the bill with the free invoice generator, or use BrickByClick Free to email it with a card payment link for $0 a month. Starter, $99 a month, adds estimates customers accept online, a job tracker and a calendar.
Sources
- Pitch factor: the Pythagorean theorem applied to a 12-inch run, as used by roofing calculators such as Jobber’s roof shingle calculator (√(rise² + run²) ÷ run).
- Bundle coverage: Owens Corning Supreme 3-tab, 33.3 sq ft per bundle (three bundles per 100 sq ft square). Always use the coverage on your product’s wrapper.
- Square foot and square metre: 1 m = 3.28084 ft, so 1 m² = 10.7639 sq ft, from NIST Handbook 44, Appendix C (General Tables of Units of Measurement).
Questions people ask
How do I calculate how many squares my roof is?
How many bundles of shingles are in a square?
What is a roof pitch factor?
How much waste should I add for shingles?
How do I measure a roof from the ground?
Does the calculator work for a hip roof?
How do I find my roof pitch?
How many square feet does a bundle of shingles cover?
Does this include ridge cap, starter strip and underlayment?
How do I turn the estimate into a price for the customer?
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