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Rafter Length Calculator — Span, Pitch, Overhang & Rafter Count

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Roof type Building horizontal span (ft) Roof pitch rise per 12 Horizontal overhang (in) Ridge board thickness (in, gable) Building length (ft, optional count) Rafter spacing on center (in)

Calculated result

14.465 ft per common rafter

11.9375 ft adjusted horizontal run · 5.9688 ft rise

1.118034 slope factor · 26.565° roof angle

1.118 ft sloped overhang extension

24 rafter positions per side · 48 total common rafters · 694.3 linear ft theoretical line length

Show the working

1. Gable run = 24 ÷ 2 − 1.5 in ÷ 24 = 11.9375 ft.
2. Slope factor = √(1 + (6 ÷ 12)²) = 1.118034.
3. Bearing line = 11.9375 × 1.118034 = 13.347 ft.
4. Overhang line = 1 × 1.118034 = 1.118 ft; total = 14.465 ft.

Geometry only. Birdsmouth/plumb cuts, ridge details, member sizing, loads and structural capacity are not determined here.

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