Roof Area Calculator
Calculate true roof surface area from building size and roof pitch angle.
How to use
- Enter the building length and width.
- Enter the roof pitch angle — take it from the design or measure it on the existing roof.
- Enter the overhang (eaves) on all sides in inches.
- The true sloped area, including wastage, appears automatically.
Note: This formula gives a good estimate for both gable and hip roofs because their sloped area equals plan area x slope factor. For complex roofs (with many valleys), split the roof into sections and calculate each one.
Frequently Asked Questions (FAQ)
What does the roof area calculator do?
It calculates the true sloped roof surface area from your building size and roof pitch angle — plan area times the slope factor, including overhang and wastage.
What do I need to enter?
Building length and width in feet, the roof pitch angle in degrees, the overhang on all sides in inches, and a wastage percentage.
Which roof shapes does it suit?
It gives a good estimate for both gable and hip roofs. For complex roofs with many valleys, split the roof into sections and calculate each one separately.
How do I find the roof pitch angle?
Take it from the design, or measure it on the existing roof.