How to use this roof area calculator
For a simple gable roof with a consistent pitch, the sloping surface area is approximately the horizontally projected roof area multiplied by the slope factor. This tool is not suitable for complex hip roofs, intersecting gables or dormers without separate measurements.
Step-by-step instructions
- Measure the building's outside length and width.
- Record the roof pitch (inches rise for 12 inches run).
- Include horizontal eave/rake overhang and a waste allowance.
Calculation formula
Important assumptions and limitations
Uniform-pitch gable roof and overhang measured horizontally on all sides. Waste depends on product, complexity and cutting pattern. Verify dimensions on site.
For material orders, confirm package yields, stock sizes and installation instructions with the actual manufacturer or supplier. Your building department determines the applicable local code; a quantity estimator is not a structural design or permit approval.
Frequently asked questions
What is one roofing square?
One roofing square equals 100 square feet of roof surface.
Can I calculate a hip roof using this?
Only as a rough gross-area estimate if the projected footprint and pitch assumptions hold. Hip cuts and details significantly change material ordering.
We publish formulas and assumptions so you can verify an estimate. Learn about our methodology or report an issue.