Calculate common rafter length from horizontal run and pitch, then add eave overhang and check stock length and preliminary count.
A common rafter’s geometric slope length is its horizontal run multiplied by √(1 + (pitch ÷ 12)²). Add a separately projected tail and verify ridge and cut details before ordering.
Common rafter length is calculated using the Pythagorean theorem: Line Length = √(Run² + Rise²) where Run is half the total building span (minus half the ridge beam thickness).
For complex roof layouts requiring trusses or prefabricated spans, compare designs with our Truss Calculator.
Calculate roof geometry and a preliminary piece count. Check structural sizing separately.
Geometric top-edge length only. Confirm ridge, plumb cut, birdsmouth, support and structural design before cutting.
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Square the run (in feet), square the rise (in feet), add them together, and calculate the square root: Length = √(Run² + Rise²). Subtract half the thickness of the ridge board and add the overhang length.
A 4:12 pitch rises 4 inches vertically for every 12 inches (1 foot) of horizontal run. Over a 12-foot run, the total roof rise is 48 inches (4 feet).
Across her work, Jamie focuses on bridging operational precision with practical technology adoption. She develops industry-specific calculators, software guides, and technical content tailored to the construction, residential living, HVAC, and artificial intelligence sectors. By pairing hands-on systems design with advanced AI and automation workflows, her resources empower trade specialists, contractors, and growing teams to eliminate bottlenecks, forecast project requirements accurately, and run more efficient operations. Fluent in five languages, Jamie approaches every tool and article with an emphasis on clarity, actionable utility, and real-world results.
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