Roof Square Footage Calculator
Estimate the sloped area of a simple roof from its horizontal footprint and pitch. Include overhangs, choose a waste allowance and calculate material coverage in square feet or square metres.
How the roof estimate works
Horizontal roof footprint = (length + 2 × overhang) × (width + 2 × overhang). Pitch multiplier = √(1 + (rise ÷ 12)²). Multiply the footprint by this multiplier to estimate the sloped surface, then apply the selected waste percentage.
For a 40 ft × 30 ft footprint with no overhang and a 6:12 pitch, the sloped area is about 1,341.64 sq ft. Adding 10% gives a material coverage estimate of 1,475.80 sq ft.
What is one roofing square?
A roofing square is 100 square feet. This tool shows coverage in roofing squares; it does not assume a fixed number of bundles per square. Use the coverage stated by your material supplier.
Will this work for a complex roof?
This is a preliminary estimate for a simple footprint with one common pitch. Dormers, valleys, openings, different pitches and irregular shapes require separate measurements. Do not double the building footprint for a simple gable roof: the pitch multiplier already accounts for the sloped surface across both sides.
Is this a roof replacement quote?
No. Optional cost is material coverage multiplied by your unit price. Labour, removal, flashing, underlayment, delivery and taxes are excluded. Confirm measurements and material requirements with a qualified roofer before ordering.
Related planning tools: Paint Calculator · Concrete Calculator.
Need to convert rise and run, an angle or slope percentage? Use the roof pitch calculator first. For attic insulation, use the insulation quantity calculator with the actual area to insulate, rather than the sloped roof area.