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Calculate rafter length from rise, run and building span — includes overhang and birdsmouth options.
Calculate rafter length from rise, run and building span — includes overhang and birdsmouth options.
Enter values above and click Calculate — results will appear here with the formula explained.
Rafter length is the hypotenuse scaled to your building's half-span, plus overhang. For a 24-foot span, half is 12 feet (144 inches) of run.
Add overhang after scaling — it extends beyond the wall, not part of the triangle.
To use the Rafter Length Calculator, enter rise (inches), run (inches), building span (feet) above for an instant result with full breakdown and formula (Rafter = sqrt(rise²+run²) × (span/2 / run) + overhang). Adjust values live to compare scenarios, then check the worked example and FAQs below for practical tips and costly mistakes to avoid.
Calculate rafter length from rise, run and building span — includes overhang and birdsmouth options. Formula: Rafter = sqrt(rise²+run²) × (span/2 / run) + overhang. Example: 6:12 pitch, 24-foot span, 12-inch overhang: rafter ≈ 13.42 feet + 1 foot = 14.42 feet.
Rafter length is the hypotenuse scaled to your building's half-span, plus overhang. For a 24-foot span, half is 12 feet (144 inches) of run.
Add overhang after scaling — it extends beyond the wall, not part of the triangle.
To use the Rafter Length Calculator, enter rise (inches), run (inches), building span (feet) above for an instant result with full breakdown and formula (Rafter = sqrt(rise²+run²) × (span/2 / run) + overhang). Adjust values live to compare scenarios, then check the worked example and FAQs below for practical tips and costly mistakes to avoid.
6:12 pitch, 24-foot span, 12-inch overhang: rafter ≈ 13.42 feet + 1 foot = 14.42 feet.
Formulas are standard public references (see our methodology). External standards are cited in the text where they apply.
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