Roof Area Calculator
Enter your building footprint and roof pitch to calculate the true sloped roof area in square feet and roofing squares.
Inputs
Formula
With overhang adjustment
Adjusted length = footprint_length + (2 × overhang)
Adjusted width = footprint_width + (2 × overhang)
Pitch factor = √(1 + (rise ÷ 12)²)
Sloped area = Adj. length × Adj. width × Pitch factor
Overhang is added to both sides of each dimension before applying the pitch factor. This accounts for the actual coverage area including eaves.
Related Tools
- Roofing Calculator — also calculates squares and shingle bundles
- Roof Pitch Calculator — pitch to degrees converter
- Roofing Squares Calculator
Frequently Asked Questions
Measure the horizontal footprint of the building (length × width), then multiply by the pitch factor for your roof slope. Pitch factor = √(1 + (rise/12)²). For a 4/12 pitch, the factor is approximately 1.054, so a 1,500 sq ft footprint yields about 1,581 sq ft of actual roof surface.
Floor area is the horizontal footprint of the house. Roof area is the actual sloped surface of the roof, which is always larger than the footprint because of the pitch. The steeper the pitch, the larger the difference.
For a hip roof, the footprint is still length × width, and the same pitch factor applies. The four triangular end sections are already accounted for when you multiply the full rectangular footprint by the pitch factor.
For material ordering purposes, yes — include the overhang in your length and width measurements because it needs to be covered. Overhangs typically add 12–24 inches on each side.