Rafter Length Calculator
Construction & Home ImprovementCalculate the length of a roof rafter from its horizontal run, roof pitch, and eave overhang.
Rafter Length
Total sloped rafter length, including the eave overhang.
Total Rise
6.50
Vertical rise over the full run, including the overhang.
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Creators
Odeh Ahwal0people find this calculator helpful
Views
Helpful
Saved
Embeds
Construction & Home Improvement calculators
Frequently Asked Questions
How is rafter length calculated from pitch?
Roof pitch is expressed as the rise in inches per 12 inches of run, for example a 6 in 12 pitch. Total horizontal run, including the overhang, is multiplied by the square root of 1 plus the pitch fraction squared, which comes directly from the Pythagorean theorem applied to the rise and run triangle.
Should the overhang be included in the run?
Yes, the rafter physically extends past the wall to form the eave overhang, so the calculator adds the overhang to the horizontal run before finding the total sloped length.
Does this account for the ridge and birdsmouth cuts?
No, this gives the theoretical rafter length along the roof slope line. Actual lumber needed is typically slightly longer to allow for the ridge cut and the birdsmouth notch at the wall plate.
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