Rafter Length Calculator

Building span (out-to-out)

Total width across the wall plates.

Roof pitch

Rise per 12" of run. Accepts 6, 7.5, or a ratio like 6:12.

Eave overhang (optional)

Horizontal projection past the wall.

Ridge board thickness (optional)

The rafter is shortened by half of this.

Rafter line length13' 4-3/16" · 4.068 m

With overhang14' 10-1/16" · 4.522 m

Run / rise12' · 3657.6 mm / 6' · 1828.8 mm

Pitch / angle6:12 · 26.6°

Plumb / seat cut26.6° / 63.4°

Length per ft of runcommon 13.42″ · hip/valley 18.00″

Common rafter runs at 26.6° — mark the plumb cut with a framing square set to 6 (rise) on the tongue and 12 (run) on the body.
Line length is 13.35 ft from the ridge to the birdsmouth (shortened 0.75″ for half the ridge).
Add 17.89″ of sloped length for the 16″ overhang.
Per foot of run: common 13.42″, hip/valley 18.00″.