Roof Pitch Calculator — Free Online Tool
Roofers quote pitch as '6/12' — but what angle is that, really? This roof pitch calculator converts your roof's rise and run into pitch, degrees, and the slope multiplier you need for material estimates.
What is the Roof Pitch Calculator?
Roof pitch is rise over a 12-inch run: a 6/12 pitch rises 6 inches for every 12 inches of horizontal run. It determines everything — material choice (asphalt shingles generally need at least 2/12, ideally 4/12 or steeper), installation method, and how walkable the roof is.
The slope multiplier is the unsung hero: multiply your home's footprint area by it to get the true roof surface area. A 6/12 roof has a 1.118× multiplier — a 2,000 sq ft footprint is actually about 2,236 sq ft of roofing to buy. Measure rise and run safely from the attic with a level, never by climbing a wet roof.
How to use this calculator
- Enter the rise in inches (the vertical measurement).
- Enter the run in inches (horizontal — usually 12).
- Click Calculate Pitch for pitch, angle, and multiplier.
Formula
Frequently asked questions
What does 6/12 roof pitch mean?
The roof rises 6 inches for every 12 inches of horizontal run — about a 26.6° angle, a common moderate pitch.
How do I measure roof pitch safely?
From inside the attic: hold a level horizontally, mark 12 inches along it, and measure the vertical distance up to the rafter. No ladder acrobatics needed.
What is the roof slope multiplier used for?
Converting footprint area into actual roof surface area, so you order the right amount of shingles, underlayment, and other materials.
What pitch is too flat for shingles?
Below about 2/12, standard shingles can leak — low-slope roofs need membrane systems like TPO or EPDM instead.