Rafter Length Calculator
Your estimate
Rafter length with overhang14 ft 5 5/8 in14.46 ft · 4.41 m
- Rafter length (no overhang)
- 13 ft 4 1/8 in13.35 ft · 4.07 m
- Run
- 11 ft 11 1/4 in11.94 ft · 3.64 m
- Rise
- 5 ft 11 5/8 in5.97 ft · 1.82 m
- Plumb cut angle
- 26.57°
- Seat cut angle
- 63.43°
Common rafter length for a gable roof, with the overhang and the plumb and seat cut angles.
Updated 2026-10-20 · Based on: roof-pitch geometry and 3 shingle bundles per square.
How to use the Rafter Length Calculator
- Enter the building span (outside of wall to outside of wall).
- Enter the pitch and the overhang measured horizontally.
- Enter the ridge board thickness (1½ in for a 2× board).
- Cut the rafter to the total length along its top edge.
Formula
Run = span ÷ 2 − ridge thickness ÷ 2. Rafter length = run × √(1 + (pitch ÷ 12)²).
Overhang along the rafter = horizontal overhang × the same multiplier. Plumb cut angle = arctan(pitch ÷ 12); seat cut = 90° − plumb.
Worked example
With the values preset in the calculator above:
- Building span
- 24 ft
- Roof pitch
- 6 in per 12 in
- Overhang (horizontal)
- 12 in
- Ridge board thickness
- 1.5 in
- Rafter length with overhang
- 14 ft 5 5/8 in (14.46 ft)
- Rafter length (no overhang)
- 13 ft 4 1/8 in (13.35 ft)
- Run
- 11 ft 11 1/4 in (11.94 ft)
- Rise
- 5 ft 11 5/8 in (5.97 ft)
- Plumb cut angle
- 26.57°
Related guides
Frequently asked questions
How long is a rafter for a 24 ft span at 6/12?
About 13 ft 4 1/8 in to the ridge plus 14 ft 5 5/8 in with a 12 in overhang.
What angle do I cut a 6/12 rafter?
Plumb cut 26.57°, seat cut 63.43°.
What size lumber for rafters?
It depends on span, spacing, snow and wood grade — use the span tables in your local code (IRC R802).
More calculators
Estimates only — check quantities with your supplier and local building code before you order.