Roofing Calculator
Estimate your roof area, the number of roofing squares and shingle bundles, and a replacement cost from your home's footprint and roof pitch.
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About the Roofing Calculator
Roofers price work by the square, which is 100 square feet of roof. This roofing calculator turns your home's footprint and roof pitch into the true roof surface area, adds a waste factor, and converts it into squares, shingle bundles and a cost estimate. Steeper roofs have more surface than the footprint alone suggests.
How to use it
- Enter the house length and width and any overhang on each side.
- Choose the roof pitch (rise per 12 inches) and a waste factor.
- Enter the installed price per square from a local quote, then press Calculate roof.
Roof area formula
Roof area = footprint × √(1 + (rise ÷ 12)2). A 6/12 pitch multiplies the footprint by 1.118. A simple gable roof on a 50 × 30 ft house with 1 ft overhangs has about 1,860 sq ft of roof.
Roof pitch factors
| Pitch | Multiplier |
|---|---|
| 4/12 | 1.054 |
| 6/12 | 1.118 |
| 8/12 | 1.202 |
| 10/12 | 1.302 |
| 12/12 | 1.414 |
What affects roof replacement cost
- Material: asphalt shingles, metal, tile or slate.
- Roof complexity, valleys, dormers and steep pitch.
- Tear-off layers, decking repairs and local labor rates.
- Permits, disposal and warranties.
Frequently asked questions
How many shingle bundles are in a square?
Three bundles of standard three-tab or architectural shingles cover one roofing square (100 sq ft).
How do I calculate roof area from the house size?
Multiply the footprint, including overhangs, by the pitch factor for your roof slope. The calculator does it automatically.
How much does a new roof cost?
Installed prices vary widely by region and material. Asphalt shingle roofs commonly run several hundred dollars per square. Get at least three local quotes.
How much waste should I add?
About 10% for simple gable roofs and 15% or more for complex roofs with hips and valleys.
Does this include tear-off?
Not unless your quoted price per square does. Ask each roofer what is included.
Last reviewed: November 2026. Estimates only. Get a written quote from a licensed roofer for exact materials and price.