Roofing
Roof Pitch Calculator
Convert roof pitch between rise-over-run, degrees and the slope multiplier used for area.
Result
Roof pitch is conventionally expressed as rise over a 12-inch run. The slope multiplier converts a flat footprint into true surface area. It is the number most area errors come from ignoring.
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About this calculator
What is a 6/12 pitch in degrees?
26.57 degrees. The roof rises six inches for every twelve inches of horizontal run, and its surface is about 1.118 times the footprint area.
What pitch is walkable?
Up to about 6/12 is generally walkable for experienced roofers. Above 8/12 usually needs roof jacks, harnesses and staging, which raises labour cost substantially.
How do I measure pitch safely?
From inside the attic, hold a level twelve inches horizontally against a rafter and measure down to the rafter at the end. That vertical distance is the rise.
The formula
slope multiplier = √(1 + (rise ÷ run)²); angle = arctan(rise ÷ run)
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