How the roof Pitch Calculator works
Roof pitch is rise over a 12 inch run: a 6/12 roof climbs 6 inches per foot. The pitch multiplier, the square root of 1 plus the slope squared, converts the flat footprint into true surface area, which is what shingle orders are based on.
Pitch = rise/run × 12 | Multiplier = √(1 + (rise/run)²)
Example: a 6/12 roof is 26.6 degrees with a 1.118 multiplier, so a 1,500 square foot footprint carries about 1,677 square feet of actual roof, roughly 17 squares of shingles before waste.
Frequently asked questions
How do I measure pitch on an existing roof?
Hold a level horizontally against the roof or a rafter, mark 12 inches along it, and measure straight down to the surface. That measurement in inches is your pitch over 12.
What pitch do shingles require?
Standard asphalt shingles need at least 2/12 with special underlayment, and 4/12 or steeper for normal installation. Below 2/12 you need membrane or metal systems.
What is a roofing square?
100 square feet of roof surface. Divide the true roof area by 100 and add about 10% waste to get the squares to order.