Calculator
Roofing Calculator
Estimate roof surface, roofing squares, shingle bundles and underlayment rolls from your house footprint, overhang and roof pitch.
Roofing is ordered in squares, and a square is 100 square feet of roof surface, not of floor. This calculator starts from the footprint you can measure on the ground, adds the eave overhang, applies the pitch of the roof and then turns the sloped area into squares, shingle bundles and, if you want, rolls of underlayment.
Project dimensions
Enter your measurements below. Results update with a waste allowance you can adjust.
Important disclaimer
This tool estimates roof surface from a rectangular footprint, an even overhang and one pitch for every roof plane. Dormers, valleys, different pitches and complex shapes need to be measured separately. Bundles per square and roll coverage come from the product you choose. Cost uses only the price you enter and excludes tear-off, flashing, ridge cap, nails, labor, tax and delivery. Confirm quantities with your supplier or roofer before ordering.
About this calculator
How the roofing calculator works
A roof is bigger than the house underneath it for two reasons. The overhang extends past the walls on every side, and the slope makes every square foot of footprint into more than one square foot of roof. The calculator handles both:
- Footprint with overhang = (length + 2 × overhang) × (width + 2 × overhang).
- Pitch multiplier = √(1 + (rise ÷ 12)²). A 6/12 roof has a multiplier of 1.1180.
- Roof surface = footprint × pitch multiplier.
- Squares = roof surface × (1 + waste% ÷ 100) ÷ 100.
- Bundles = squares × bundles per square, rounded up.
The same multiplier applies to gable and hip roofs as long as every plane has the same pitch, because each plane rises at the same rate over the footprint below it.
Worked example
A house measures 40 by 30 feet with a 1 foot overhang and a 6/12 roof. The footprint with overhang is 42 × 32 = 1,344 square feet. Multiplied by 1.1180, the roof surface is 1,502.64 square feet. With a 10 percent waste allowance that becomes 1,652.9 square feet, or 16.53 squares. At 3 bundles per square the order is 50 bundles. The eave and rake edge around the roof is 148 feet, which is useful for drip edge and starter strip.
The same house with no overhang and a 4/12 roof comes to 1,264.91 square feet of roof, 13.91 squares with allowance and 42 bundles.
Pitch multipliers at a glance
| Pitch | Angle | Multiplier |
|---|---|---|
| 2/12 | 9.46° | 1.0138 |
| 3/12 | 14.04° | 1.0308 |
| 4/12 | 18.43° | 1.0541 |
| 5/12 | 22.62° | 1.0833 |
| 6/12 | 26.57° | 1.1180 |
| 7/12 | 30.26° | 1.1577 |
| 8/12 | 33.69° | 1.2019 |
| 9/12 | 36.87° | 1.2500 |
| 10/12 | 39.81° | 1.3017 |
| 12/12 | 45.00° | 1.4142 |
Choosing a waste allowance
A simple gable roof with few penetrations can work with about 10 percent. Hip roofs, valleys, dormers and skylights create more cut shingles, so 15 percent or more is common. Starter strip and ridge cap are usually separate products and are not part of the bundle count.
What this calculator does not include
- Different pitches on different parts of the roof. Measure each section and add the results.
- Ridge cap, starter strip, drip edge, flashing, vents, nails and ice and water shield.
- Tear-off of the old roof, decking repairs, labor and disposal.
Frequently asked questions
How many bundles are in a square?
Many architectural and three-tab shingles are packed at 3 bundles per square, but some heavier products use 4 or 5. The wrapper states the coverage, so enter that figure.
Can I measure the roof from the ground?
Yes. Measure the outside walls of the house, add the overhang and use the pitch. That avoids climbing onto the roof, and the pitch can be measured from inside the attic or with the roof pitch calculator.
Why does my roofer quote more squares?
Roofers measure every plane, add waste for the roof shape, and often include starter, ridge and extra for complex details. A difference of 10 to 15 percent is common on roofs with valleys and hips.
For a step-by-step walkthrough, read How Many Squares of Shingles Do I Need?
Related guides
Practical planning guides paired with this calculator.