How to use the roofing calculator
- Measure the house footprint. Enter the outside length and width of the house in feet. You can measure on the ground; you do not need to climb on the roof.
- Add the overhang. Eaves usually stick out 12 to 24 inches past the walls on every side. The calculator adds it to both dimensions.
- Choose the pitch. Pitch is how many inches the roof rises for every 12 inches across. Not sure? Use our roof pitch calculator.
- Pick the roof type and waste. Gable roofs need about 10% extra. Hip roofs have more cuts at the hips and valleys, so the calculator switches to 15%.
Roof area formula
A sloped roof has more surface than the flat footprint under it. The pitch multiplier converts one to the other:
Pitch multiplier = √(1 + (pitch ÷ 12)²)
Roof area = footprint × pitch multiplier
Squares = roof area ÷ 100
For a simple gable or hip roof with the same pitch on every side, this gives the same total area. Dormers, valleys and multiple roof levels add material, so measure those sections separately if they are large.
Pitch multipliers
| Pitch | Angle | Multiplier |
|---|---|---|
| 3/12 | 14.0° | 1.031 |
| 4/12 | 18.4° | 1.054 |
| 6/12 | 26.6° | 1.118 |
| 8/12 | 33.7° | 1.202 |
| 10/12 | 39.8° | 1.302 |
| 12/12 | 45.0° | 1.414 |
Worked example
A 50 × 30 ft house with 12 inch eaves has a footprint of 52 × 32 = 1,664 sq ft. With a 6/12 pitch the multiplier is 1.118, so the roof area is about 1,860 sq ft, or 18.6 squares. Add 10% waste for 20.5 squares. Architectural shingles come 3 bundles to the square, so order 62 bundles and 3 rolls of synthetic underlayment.
What does a new roof cost?
Installed prices vary widely by region, material and roof complexity. As a rough guide, asphalt shingle roofs often fall in the range of a few hundred to around a thousand dollars per square installed, including tear-off and disposal, while metal, tile and slate cost several times more. Enter a local quote per square in the calculator to see the total for your roof, and always get at least three written estimates.
Shingle and roofing terms
- Square: 100 square feet of roof surface. Roofers price and order by the square.
- Bundle: a pack of shingles. Most three-tab and architectural shingles need 3 bundles per square; some heavy designer shingles need 4 or 5.
- Underlayment: the water-resistant layer under the shingles. Synthetic rolls typically cover 10 squares; 15 lb felt covers about 4.
- Starter strip and ridge cap: special shingles for the eaves and ridges, ordered by the linear foot.
Frequently asked questions
How many bundles of shingles do I need for 1,000 square feet?
1,000 square feet is 10 squares. At 3 bundles per square that is 30 bundles, plus about 10% waste, so order 33 bundles.
How do I calculate roof squares?
Multiply the house footprint including overhangs by the pitch multiplier to get the sloped roof area, then divide by 100. Each 100 square feet is one roofing square.
How much extra shingles should I buy?
Add about 10% for a simple gable roof and 15% for hip roofs or roofs with many valleys, dormers and cuts.
Does roof pitch change how many shingles I need?
Yes. The steeper the roof, the larger its surface compared with the footprint. A 12/12 roof has about 41% more area than its footprint, while a 4/12 roof has only about 5% more.
How many squares is a 2,000 square foot house?
It depends on the footprint, overhangs and pitch, not the living area. A single-story 2,000 sq ft home with 12 inch eaves and a 6/12 pitch usually has around 23 to 25 squares of roof.
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Last updated October 2026.