Roofing Calculator: Squares, Shingles & Materials
Estimate roof area, roofing squares, shingle bundles, underlayment rolls, ridge cap and drip edge for a gable or hip roof from the building footprint and pitch.
A roof's true area is its footprint times a pitch factor: 1.118 at 6/12 and 1.414 at 12/12. One roofing square is 100 sq ft, about 3 bundles of shingles. A 28 × 40 ft house at 6/12 has about 12.5 squares, so roughly 42 bundles with 10% waste.
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How to use a roofing calculator: roof area, squares and shingles
A pitched roof is bigger than the footprint of the building beneath it. The steeper the pitch, the more surface there is to cover. Multiply the footprint (including overhangs) by a pitch factor to get the true roof area.
roof area = footprint × pitch factor
squares = roof area × (1 + waste) ÷ 100
bundles = squares × 3
Roofers measure in squares: one square equals 100 square feet. Architectural asphalt shingles usually come three bundles to a square.
Pitch multiplier chart
| Pitch | Multiplier | Angle |
|---|---|---|
| 2/12 | 1.014 | 9.5° |
| 3/12 | 1.031 | 14.0° |
| 4/12 | 1.054 | 18.4° |
| 5/12 | 1.083 | 22.6° |
| 6/12 | 1.118 | 26.6° |
| 7/12 | 1.158 | 30.3° |
| 8/12 | 1.202 | 33.7° |
| 9/12 | 1.250 | 36.9° |
| 10/12 | 1.302 | 39.8° |
| 12/12 | 1.414 | 45.0° |
How to find your roof pitch
Place a level 12 inches along a rafter in the attic and measure straight up to the rafter. That vertical distance in inches is the rise (6 inches = 6/12 pitch). From the ground, you can also hold a level against the roof edge or use a phone inclinometer app.
How much waste should you allow?
| Roof type | Waste |
|---|---|
| Simple gable | 10% |
| Hip roof | 12% |
| Valleys, dormers, chimneys | 15% or more |
What else does a roof need?
Besides shingles you'll need underlayment, starter strips along the eaves, ridge cap shingles, drip edge, flashing, roofing nails, vent boots and, in cold climates, ice-and-water shield along the eaves and valleys. Steep roofs (8/12 and up) are dangerous to walk, so many homeowners hire a pro; use this estimate to check contractor quotes.
Walls under the roof? See the siding and insulation calculators.
Frequently asked questions
How many bundles of shingles are in a square?
Most architectural and 3-tab shingles come three bundles to a square (100 sq ft). Some premium or heavy shingles are four bundles per square.
How many bundles of shingles do I need for a 2,000 sq ft roof?
A 2,000 sq ft roof is 20 squares, so about 60 bundles; with 10% waste, 66 bundles.
How do I find my roof pitch?
Measure the rise over 12 inches of horizontal run with a level and tape. 6 inches of rise over 12 inches of run is a 6/12 pitch.
How much waste should I add for roofing?
Add about 10% for a simple gable roof, 12% for hip roofs, and 15% or more for valleys, dormers or complex shapes.
How many squares are in a roof?
Divide the total roof area in square feet by 100. A 28 × 40 ft footprint at 6/12 pitch is about 12.5 squares before overhangs and waste.
How long does a roof take to shingle?
A typical house takes a crew 1–3 days; DIY can take a week or more depending on size and pitch.
How much does roofing cost per square?
Asphalt shingle roofs are commonly quoted at several hundred dollars per square installed, varying widely by region, pitch and tear-off. Get local bids.
Does this calculator work for a flat or metal roof?
The area result does. For a flat roof, pitch 2/12 gives a multiplier near 1.0; use the area to order membrane, rolled roofing or metal panels instead of shingles.
Sources and further reading
- Asphalt Roofing Residential Manual: design and application methods — Asphalt Roofing Manufacturers Association (2014)
- National Roofing Contractors Association — NRCA: roofing guidelines
These references support the general guidance on this page. The calculator applies the standard formulas shown above to the numbers you enter.
Related calculators
. Estimates only. Always confirm quantities with your supplier or a qualified contractor before ordering, and add extra for waste and site conditions.