🏠 Roofing Calculator
A pitched roof has more surface than its footprint: the steeper the pitch, the bigger the multiplier. Enter the building's length, width and roof pitch to get the true roof area.
Results are in roofing squares (100 sq ft each) with 10% waste included — the standard allowance for cuts and valleys.
How to use this calculator
Enter your roof's length, width and pitch to get the true roof area and the number of shingle squares to order with waste included.
- Measure the roof's length and width in feet.
- Pick the Roof pitch, like 6/12.
- The results appear instantly.
- Read the squares to order, with 10 percent waste already included.
Frequently asked questions
How does pitch change the area?
A pitched roof is larger than its footprint. The calculator multiplies length times width by the square root of 1 plus the pitch-over-12 squared, the exact slope factor.
Can you give a worked example?
A 40 by 30 foot roof at 6/12 pitch has 1341.64 square feet of surface, which is 13.42 squares, so you order 15 squares with the 10 percent waste allowance.
What is a roofing square?
One square covers 100 square feet. Shingles are sold by the square, so the industry thinks in these units.
Is 10 percent waste enough?
For simple gable roofs, yes. Complex roofs with many valleys and hips can need 15 percent, so round up generously on cut-up designs.