Roofing Calculator
Estimate roof surface area, roofing squares, and asphalt shingle bundles from home dimensions and roof pitch.
How It's Calculated
Formula
\text{roofArea} = \text{length} \times \text{width} \times \text{pitchFactor} \\ \text{squares} = \frac{\text{roofArea}}{100}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 a V1 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 V1 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.