📐 Free Calculator
Rafter Length Calculator
Calculate common rafter length for roofs using pitch, run, and overhang. Determine rafter length, rise, and angles for construction.
Half of total building width (excluding overhang)
Subtracted from total length (typical 1.5″ for 2x lumber)
Subtract half of ridge thickness from run if using ridge board
📏 Common Rafter Length
0 ft 0 in
📐 Rafter length formula: Rafter Length = √(Run² + Rise²). Rise = Run × (Pitch ÷ 12). Overhang adds extra length. Deduct birdsmouth cut and ridge board adjustment.
💡 Pro tip: Always cut one test rafter first. Add 10-15% for waste when ordering lumber. Use this calculator for common rafters only — hip/valley rafters require different calculations.