Roof Calculator

How the Roof Calculator Works

Enter the horizontal dimensions of your roof, its pitch and (optionally) the overhang. The calculator converts the flat footprint into the true sloped surface area using the pitch multiplier, then expresses the result in square feet and roofing squares.

Formulas

• Footprint = (Length + 2 × Overhang) × (Width + 2 × Overhang)
• Slope Factor = √(1 + (Rise / Run)²)
• Roof Surface Area = Footprint × Slope Factor
• Roofing Squares = Roof Surface Area ÷ 100

Worked Example

50 ft × 30 ft with a 6/12 pitch: footprint = 1,500 sq ft, slope factor = 1.118, surface area ≈ 1,677 sq ft ≈ 16.8 roofing squares.

What You Need

Your building's outside length and width, plus the roof pitch. Measure the footprint from the ground if the plan is simple; measure pitch in the attic with a level and a tape measure, or start with our Roof Pitch Calculator. Leave overhang at 0 if you only want the covered area.

Assumptions & Limitations

Models a simple rectangular roof section. Roof type is recorded for future refinement — in this version the geometry math is identical for gable, hip, shed and flat shapes. Complex roofs should be calculated section by section and summed.