Rafter Calculator
Calculate common-rafter length from building span or horizontal run, roof pitch and optional horizontal overhang.
Results
Horizontal run
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Rise to ridge
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Rafter length to wall
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Rafter length including overhang
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Roof angle
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Use the result as a planning estimate and verify project-specific measurements, manufacturer information and local requirements where relevant.
How it works
The calculator converts the pitch to a slope factor and applies it to the horizontal run. The optional overhang is treated as additional horizontal run.
rafter length = horizontal run × √(1 + (rise/12)²)Limitations
- This is geometric layout only. It does not size rafters, account for ridge/seat-cut shortening, or certify structural or code compliance.