Roofing and Roof Pitch Calculator
Estimate roof area in squares from the footprint and pitch, with waste, bundles of shingles and the pitch in degrees, for roofing quotes. It is an estimate to quote from, not a substitute for measuring the roof.
Your numbers
Measured out from the wall. Added on every side of the footprint.
For your notes: at one pitch, gable and hip use the same multiplier.
10% is a common starting point; cut-up hip roofs need more.
Usually 3. Check the wrapper.
Roof squares, before waste
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- Roof area
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- Footprint with overhang
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- Pitch multiplier (6/12)
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- Squares with 10% waste
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- Bundles of shingles to order
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- Those bundles cover
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An estimate for quoting, not a measurement: dormers, valleys and planes at different pitches change the real number.
Gable or hip, the multiplier is the same when every plane has the same pitch. Ridge cap, starter strip and underlayment are ordered separately.
The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.
How roof area is worked out
Start with the footprint the roof covers, seen from above: the house length and width plus the overhang on every side. Then multiply by the pitch multiplier, which accounts for the slope: a pitched roof has more surface than the flat footprint under it. Divide by 100 to get squares, the unit roofers order in.
Take a 40 × 30 ft house with a 12 in overhang. The footprint is 42 × 32 = 1,344 sq ft. At a 6/12 pitch the multiplier is 1.118, so the roof is about 1,502.6 sq ft, or 15.03 squares. With 10% waste that is 16.53 squares, which rounds up to 50 bundles at three to the square.
Gable or hip makes no difference to the multiplier when every plane has the same pitch: the footprint of each plane is its own area times the cosine of the slope, whatever its shape. Roofs with mixed pitches, dormers or porches need each section worked out on its own and added up.
Roof pitch chart
Pitch is the rise in inches for every 12 inches of run. The table below is worked out from the formulas: angle = atan(rise ÷ 12), slope = rise ÷ 12 × 100, multiplier = √(1 + (rise ÷ 12)²).
| Pitch | Angle | Slope | Multiplier |
|---|---|---|---|
| 1/12 | 4.8° | 8.3% | 1.003 |
| 2/12 | 9.5° | 16.7% | 1.014 |
| 3/12 | 14° | 25% | 1.031 |
| 4/12 | 18.4° | 33.3% | 1.054 |
| 5/12 | 22.6° | 41.7% | 1.083 |
| 6/12 | 26.6° | 50% | 1.118 |
| 7/12 | 30.3° | 58.3% | 1.158 |
| 8/12 | 33.7° | 66.7% | 1.202 |
| 9/12 | 36.9° | 75% | 1.250 |
| 10/12 | 39.8° | 83.3% | 1.302 |
| 11/12 | 42.5° | 91.7% | 1.357 |
| 12/12 | 45° | 100% | 1.414 |
How to measure roof pitch safely
From the attic: hold a level flat against the underside of a rafter, mark 12 inches along the level, and measure straight up from that mark to the rafter. The distance in inches is the rise, so 6 inches means a 6/12 pitch. If you can only measure an angle, the Roof pitch mode above converts it.
From the ground: a pitch or angle app that reads the slope from a photo of the gable end gives a fair figure for an estimate. Do not climb onto the roof to measure it. Leave anything on the roof to a crew with fall protection, and treat this page as an estimate to quote from, not a substitute for their measurement.
Squares, bundles and waste
A roofing square is 100 sq ft of roof. Most asphalt shingles come three bundles to the square, but coverage varies by product, so check the wrapper: Owens Corning lists three bundles covering 100 sq ft for its Supreme 3-tab shingles and three bundles covering 98.4 sq ft for its TruDefinition Duration architectural shingles. If a product lists a different count, change the bundles per square above.
Waste covers the shingles cut at edges, hips and valleys. A common rule of thumb is 10 to 15%, toward the top of the range on cut-up roofs. Ridge cap, starter strip, underlayment and flashing are ordered separately.
Tips for the walkthrough with the homeowner
Measure the footprint on the ground, confirm the pitch from the attic, and photograph each roof plane and any damage. Run the numbers here while you are still on site, so the homeowner hears a range before you leave.
Then write down what the homeowner told you: where it leaks and since when, what they want to spend, when they need the work done, and who else is deciding. Those notes decide the quote as much as the squares do.
Sources, checked September 2026:
More for roofing and home-services reps: Roofing sales training, Door-to-door sales, Solar sales.
The numbers are half the quote
The measurements go in the quote; what the homeowner said about leaks, budget and timing goes in ParrotNotes: record the walkthrough and get the summary and next steps.
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