Roof Square Footage Calculator
Your roof is larger than your home's footprint because of its slope. Enter a couple of numbers to estimate your roof area, the number of "squares," and how many shingle bundles you'll need.
The ground area covered by your roof — usually close to your home's square footage (single storey) or the area of the upper floor's footprint.
Estimated roof area
Total area to cover (incl. waste)
Estimate only. Pitch, overhangs, valleys, hips and dormers all affect the real total. For an exact figure and material list, request a free measurement.
How the roof area calculation works
A roof is almost always bigger than the floor area beneath it, because it slopes. To get the real surface area, you take your home's footprint (the flat ground area under the roof) and multiply it by a slope factor that depends on the roof's pitch.
Pitch is written as "rise over run" — how many inches the roof rises for every 12 inches it runs horizontally. A 6/12 roof rises 6 inches per foot. The steeper the pitch, the larger the slope factor:
| Roof pitch | Slope multiplier | Adds roughly |
|---|---|---|
| 4/12 | 1.054 | +5% |
| 6/12 | 1.118 | +12% |
| 8/12 | 1.202 | +20% |
| 10/12 | 1.302 | +30% |
| 12/12 | 1.414 | +41% |
Then we convert to roofing squares (1 square = 100 sq ft) and estimate shingle bundles at the standard 3 bundles per square. We add a waste allowance because every roof needs extra material for cuts, starter rows, hips, valleys and ridge caps.
This tool is great for ballpark budgeting, but ordering materials off an estimate is risky. A roofer's measurement (or an aerial measurement report) accounts for every plane, penetration and overhang.
Roof calculator FAQs
How do I find my roof square footage?
Measure your home's footprint (length × width of the area under the roof), then multiply by a slope factor based on your roof pitch. A flat-ish 4/12 roof adds about 5%, while a steep 12/12 roof adds about 41%. Our calculator does this for you.
What is a "roofing square"?
A roofing square equals 100 square feet of roof area. Roofers price and order materials by the square, so a 2,000 sq ft roof is 20 squares.
How many shingle bundles are in a square?
Most architectural and 3-tab shingles come 3 bundles per square. So a 20-square roof needs roughly 60 bundles, plus extra for waste and starter/ridge.