Rafter Length Calculator

Enter your rafter run, roof pitch, and overhang to calculate the exact rafter length, rise, cut angles, and which standard lumber length to purchase.

Roof Pitch

Rafter Run (ft)

Overhang / Tail (in)

Ridge Thickness (in)

HAP / Seat Cut Depth (in)

Rafter Section

Hover for details • not to scale

Total Rafter Length

14' 6"

14.46 ft (with overhang)

Rise

6' 0"

5.97 ft vertical

Line Length (no overhang)

13' 4"

13.35 ft

Overhang Length

1' 1"

1.12 ft along slope

Plumb Cut Angle

26.6°

from vertical

Seat Cut Angle

63.4°

from horizontal

Buy 16-foot lumberYour total rafter length of 14' 6" rounds up to a standard 16-foot board. Standard lumber lengths are 8, 10, 12, 14, 16, 18, and 20 feet — always buy the next size up to allow for clean end cuts.

HAP (Height Above Plate): 3.5" seat cut depthThe birdsmouth cut will leave 3.5" of rafter material above the wall plate. A common rule of thumb is that the seat cut should not exceed one-third of the rafter depth. Verify your HAP meets local code requirements.

This calculator provides theoretical rafter dimensions based on standard geometry. Always verify measurements on site and consult local building codes — actual conditions (lumber dimensions, ridge beam details, load requirements) may require adjustments.