Roofing Calculator
Estimate roof surface area, roofing squares, and asphalt shingle bundles from home dimensions and roof pitch.
Calculator Inputs
Base building plan length, in feet. Must be a positive number.
Base building plan width, in feet. Must be a positive number.
Multiplier that converts flat plan area to sloped roof area (1.0 = flat; a 4:12 pitch is about 1.054, a 6:12 pitch is about 1.118). Must be a positive number.
- Roof Surface Area
- 1,341.60
- Roofing Squares
- 13.42
- Asphalt Shingle Bundles (est.)
- 41
About these results
CalcSpectrum calculators produce automated estimates using established formulas and the specific values you enter. Because real-world outcomes depend on input accuracy, mathematical assumptions, and rounding conventions, please verify critical figures with an appropriately qualified financial, tax, medical, legal, or other professional, as relevant.
How It's Calculated
Formula
This calculator estimates roof surface area for a simple rectangular (gable-style) home plan. The base plan area (length times width) is multiplied by a pitch slope factor to approximate the sloped roof surface — a steeper roof has more surface area than its flat footprint. The result is also expressed in roofing "squares" (1 square = 100 sq ft, the standard roofing trade unit), and an estimated bundle count assuming standard 3-tab/architectural asphalt shingle packaging of 3 bundles per square. This is an estimate for simple gable roofs — it does not model hips, valleys, dormers, or other complex roof geometry, and the bundle count is specific to asphalt shingles; other roofing materials use different packaging.
Worked Examples
40 ft x 30 ft home, 6:12 pitch (factor 1.118)
- Base plan area = 40 x 30 = 1,200 ft²
- Roof area = 1,200 x 1.118 = 1,341.6 ft²
- Squares = 1,341.6 / 100 = 13.416
- Bundles = ceil(13.416 x 3) = 41
Flat pitch factor (1.0)
- Base plan area = 40 x 30 = 1,200 ft²
- Roof area = 1,200 x 1.0 = 1,200 ft²
- Squares = 12
Frequently Asked Questions
Does this handle hip roofs, valleys, or dormers?
No. This is a narrow estimate for a simple rectangular gable-style roof plan. Complex roof geometry with hips, valleys, or dormers needs a more detailed take-off than a single pitch factor can represent.
Why 3 bundles per square?
Three bundles per square is the standard packaging convention for most 3-tab and architectural asphalt shingles — each bundle covers roughly a third of a 100 sq ft square. It is not universal: some shingle lines and non-shingle materials (metal, tile) use different packaging, so treat the bundle count as an asphalt-shingle estimate.
Where do I find my roof's pitch factor?
The pitch factor is a multiplier for a given roof slope (rise over a 12-inch run) — for example, roughly 1.054 for a 4:12 pitch and roughly 1.118 for a 6:12 pitch. A flat roof uses a factor of 1.0.