12/12 Roof Pitch

What a 12/12 pitch looks like on the jobsite

12/12 is 45°, the pitch at which rise equals run exactly. A common "signature" pitch for steep-style architecture.

Common use cases:

• A-frames and chalets
• Steep-style dormers

Rafter length by run

Multiply the common rafter run (half the building width) by 1.4143. That is the rafter length before you add any tail overhang. The table below shows a few common runs:

Add rafter tail length (typically 12 to 24 inches) if you want the full ridge-to-tail dimension.

Laying it out with a Speed® Square

This is the One Number® method from the Blue Book of Rafter Lengths, the pocket reference Albert Swanson packaged with the first Speed® Square in 1925.

1. 1Pivot the square on the top edge of the rafter. Find 12 on the common scale and align it with the top edge. Scribe a plumb line, that is the ridge cut.
2. 2From the long point of the plumb, measure run × 1.4143 along the top edge to locate the seat cut.
3. 3At the seat mark, scribe a plumb at the same 12 common reference, then a level line equal to the top-plate width. Cut both ends and test-fit.

Nearby pitches

• 10/12 pitch

  39.81° · 83.33%

  →

• 11/12 pitch

  42.51° · 91.67%

  →

• 13/12 pitch

  47.29° · 108.33%

  →

• 14/12 pitch

  49.4° · 116.67%

  →