Roof area calculator.
Enter your building footprint and roof pitch — get the sloped roof area, plus the total square footage you'll need to cover with material once waste is included.
How to use this calculator
- Measure your building footprint — the area of the house outline as seen from above. For a simple rectangular house, this is length × width.
- Pick your roof pitch — the rise over run, e.g. 6/12 means the roof rises 6 inches for every 12 inches horizontal. If you don't know your pitch, 4/12–6/12 is the most common range for US homes.
- Add your waste factor — 10% is the default for simple roofs, 15% for moderate complexity, 18–20% for hips and complex layouts.
- Read your roof area — the calculator shows total sloped area and area with waste included. Use the latter when ordering materials.
Roof area questions, answered.
How do I calculate roof area from a building footprint?
Multiply the building footprint area by the pitch multiplier. A flat roof has a multiplier of 1.0; a 5/12 pitch is ~1.083; a 12/12 pitch is ~1.414. The result is the actual sloped roof surface area you'll need to cover with material.
What pitch multiplier should I use?
Use the table built into the calculator. Common values: 3/12 = 1.031, 4/12 = 1.054, 5/12 = 1.083, 6/12 = 1.118, 8/12 = 1.202, 10/12 = 1.302, 12/12 = 1.414. These are the secant of the slope angle.
How much waste factor should I add?
10–12% is standard for architectural shingles on a typical 4/12–8/12 roof. Add 15% for complex roofs with valleys and dormers. Add 18–20% for hip roofs or anything with lots of cuts. Metal and tile usually require slightly less (8–10%) because cuts are minimized.
Is this calculator accurate enough for an estimate?
For a rough back-of-envelope estimate, yes. For a binding quote, you want to either climb the roof or use satellite-traced measurement (which is what our full app does in 3 seconds from any address).
Skip the manual math — SatelliteQuotes does this in 3 seconds.
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