Rafter Calculator

A three-stud corner adds two studs beyond the one the layout already places there; a two-stud California corner adds one.
A king stud and a jack (trimmer) stud each side is four. Cripples above and below are extra and are not counted here.
Half of it is deducted from each rafter run. A dressed 2x is 1.5 in thick under PS 20.
Rafter length including overhang
14.4646 ft
Wall Stud & Rafter Calculator
Pieces needed
32
Pieces from the spacing alone
16
Extra pieces for corners, intersections and openings
0
Rafter line length, ridge to plate
13.3465 ft
Rafter run
11.9375 ft
Rafter rise
5.9688 ft
Rafter length per foot of run
1.118034
Roof angle from horizontal
26.565 deg
Plumb cut from square
26.565 deg
Total linear feet of member
462.87 ft
Cost of the pieces
0.00 USD
Worked out from International Residential Code (IRC), Chapter 6 Wall Construction and Chapter 8 Roof-Ceiling Construction and 2 other sources.
Lengths are theoretical line lengths to the outside of the plate; they do not include the birdsmouth seat cut, the tail cut or any ridge-beam drop.
A quantity and geometry take-off only. It does not size any member and does not check spans, loads, bracing, uplift connections or header sizes; those must come from a licensed engineer’s design or from the prescriptive span tables of the code adopted where you build (e.g. IRC Tables R602.3(5) and R802.4).

How this is worked out

5 steps
  1. Run = span/2 - half the ridge = 24/2 - 0.75 in = 11.9375 ft.
  2. A 6/12 pitch has slope factor sqrt(1 + (6/12)^2) = 1.118034.
  3. Line length = 11.9375 x 1.118034 = 13.3465 ft; with a 1 ft overhang measured level, the rafter is 14.4646 ft long.
  4. Roof angle = atan(6/12) = 26.565 degrees, which is also the plumb-cut angle marked from square.
  5. Rafters: floor(240 / 16) + 1 = 16 per slope, two slopes = 32.

Results are general information, not financial, tax, legal, medical or engineering advice.