COMPREHENSIVE FRAMING UTILITY
Rafter Calculator
Calculate common rafter dimensions from total building span or horizontal run, including vertical rise, roof angle, base length, and overhang extension.
Rafter Calculator
Calculate common rafter dimensions from total building span or horizontal run and pitch.
feet
Total distance from outside wall to outside wall.
/ 12
inches
Span vs. Run in Rafter Framing
When framing a gable roof, building span is the total exterior width of the building, while horizontal run is the distance from the outside top plate to the centerline of the ridge board (Span ÷ 2).
Formulas
Horizontal Run = Building Span ÷ 2
Rise = Run × (Pitch ÷ 12)
Total Rafter = (Run + Overhang) × √(1 + (Pitch ÷ 12)²)