Enter span, ridge length, pitch, and overhang rafter lengths in ft-in-fractions, cut angles, and stock size solve live.
Roof pitch26.57°
Total rafter blank length
16′ 8-7/16″
BLANK
Bill of materials+0% waste
Common rafter ridge to bird's-mouth
Pitch angle 26.57°
Net 167.25″ run · 6/12 · Waste —
Eave overhang cut
Along the rafter slope
Net 12″ horizontal · Waste —
Total rafter blank
Buy 18-ft stock
Net Line + overhang · Waste —
Bird's-mouth cuts
3.5″ level seat · under ⅓ of 2x8 depth
Net Plumb 26.57° · Seat 63.43° · Waste —
Rafter count 16″ O.C.
Both slopes · +1 starter pair
Net 40 ft ridge · Waste —
Cost projection
Saved on this device · No account · No cloud
Total · $1,364.00
18′ stock 62 rafters
The rafter run is half the building span minus half the ridge board thickness; line length = √(run² + rise²), where rise = run × (pitch ÷ 12).
Enter span, ridge length, pitch, and overhang rafter lengths in ft-in-fractions, cut angles, and stock size solve live.
The plumb cut angle equals the pitch angle (arctan(pitch ÷ 12)); the seat cut is 90° minus the pitch angle.
A 3.5 in level seat on the plate cuts a plumb depth of 3.5 × tan(pitch angle) it must stay under one-third of the rafter depth or the rafter is overcut.
Eave overhang is measured horizontally past the plate; its rafter length is √(overhang² + (overhang × pitch ÷ 12)²).
L = run × √(1 + (rise/12)²)
The run is 168 in minus half the ridge (167.25 in); rise = 167.25 x 0.5 = 83.6 in. Line length = sqrt(167.25^2 + 83.6^2) = 187 in, about 15 ft 7 in. Add the overhang cut and buy 18-ft stock.
The plumb cut is the pitch angle — 26.57 degrees for 6/12 — and the seat cut is 90 - 26.57 = 63.43 degrees. A 3.5 in seat cuts 1.75 in deep, safely under the 1.83 in limit for 2x6 stock.
Ceil(480 / 16) + 1 = 31 pairs, or 62 rafters for both slopes, plus a starter pair at each gable end in practice.
The plumb depth of the seat cut is 3.5 x tan(pitch angle) and must stay under one-third of the rafter depth — otherwise the rafter is overcut and weakened.
Horizontally past the outside of the plate. Its rafter length is sqrt(overhang^2 + (overhang x pitch / 12)^2), added to the line length before rounding up to stock.
Keep estimating
More framing calculators for this job.