Rafter Length Calculator
Calculate common rafter length for a gable roof from building span, roof pitch and eave overhang.
Enter your values and press Calculate.
How to use the Rafter Length calculator
Lumber comes in 2-ft increments, so round the rafter up to the next even length.
Formula
Rafter = (span ÷ 2 + overhang) × √(1 + (pitch ÷ 12)²). Subtract half the ridge-board thickness for the exact cut length.
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