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Rafter Length Calculator - Calculate rafter length and cuts for roof framing
Calculate rafter length and cuts for roof framing
Formulas and edge cases are reviewed against authoritative references before publication. For methodology, editorial standards, or corrections, use the links below.
Frequently asked questions
How is pitch expressed?
As rise over run, e.g., 6/12 means 6 inches of rise per 12 inches of horizontal run.
What about the ridge board?
Subtract half the ridge board thickness from the run for accurate rafter length.
How to mark cuts?
Use a framing square with pitch numbers to mark plumb and seat cuts accurately.
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About this tool
This Rafter Length Calculator turns your inputs into practical results. Provide Roof Span, Roof Pitch, and Overhang Length to calculate Rise Height and Rafter Length.
Adjust values to compare scenarios and see how sensitive the result is. The calculation uses the numbers as entered, so double-check units and expect small differences from rounding in the displayed totals.