Enter the length and width of your house including the overhangs, choose the roof shape and pitch, and get the roof area in squares, the bundles of shingles to buy, and the underlayment, drip edge, starter strip and ridge cap.
Underlayment, ridge cap and cost
Most architectural and 3-tab shingles come 3 bundles to a square, but some take 4. Check the coverage on the wrapper.
How the calculator works
- Roof area = house length × width (with overhangs) × pitch factor
- Squares = roof area ÷ 100, plus extra for waste
- Bundles = squares × 3
A roofing square is 100 square feet of roof. Measuring the footprint from the ground and multiplying by the pitch factor is safer than climbing onto the roof, and it works for gable and hip roofs with one pitch.
Pitch factor
| Pitch | Pitch factor |
|---|---|
| 3/12 | 1.031 |
| 4/12 | 1.054 |
| 5/12 | 1.083 |
| 6/12 | 1.118 |
| 7/12 | 1.158 |
| 8/12 | 1.202 |
| 9/12 | 1.250 |
| 10/12 | 1.302 |
| 12/12 | 1.414 |
Not sure of your pitch? Use the roof pitch calculator.
Worked example
A house 40 ft × 30 ft including overhangs, with a 6/12 gable roof:
- 40 × 30 × 1.118 = 1,342 square feet of roof
- With 10 percent extra: 14.8 squares
- Bundles: 14.8 × 3 = 45 bundles
- Drip edge: 80 ft of eaves + 67 ft of rakes = 147 ft
- Ridge cap: 40 ft
As a hip roof with the same size and pitch, you’d add 15 percent extra for the extra cuts, which is 15.4 squares or 47 bundles, with about 100 ft of ridge and hips to cap.
How much extra to add
- Simple gable roof: about 10 percent.
- Hip roof: about 15 percent.
- Valleys, dormers and many angles: 15 to 20 percent or more.
Roofing accessories
- Underlayment: synthetic rolls often cover around 10 squares; #15 felt about 4 and #30 felt about 2. Check the roll label.
- Drip edge: goes along the eaves and rakes, usually sold in 10 ft pieces.
- Starter strip: goes along the eaves, and many roofers also run it up the rakes.
- Ridge cap: covers ridges and hips. Coverage per bundle varies by product, so enter it in the calculator.
Frequently asked questions
How many bundles of shingles do I need?
Work out the roof area in squares, add extra for waste, and multiply by 3 for most shingles. A 15 square roof needs about 45 bundles.
How many squares is my roof?
Multiply the house footprint, including overhangs, by the pitch factor and divide by 100.
How many bundles are in a square?
Usually 3, but some heavier architectural shingles take 4. Check the coverage printed on the bundle.
How do I measure a roof without getting on it?
Measure the length and width of the house including the overhangs, find the pitch from the gable end or the attic, and use the pitch factor.
Does this work for complex roofs?
For a single pitch, yes. For roofs with different pitches or many sections, work out each section separately and add them up.
Results are estimates for planning. Check product coverage and local code. See How We Calculate for the formulas we use.
Guides for this project
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