Four extra studs is two kings and two trimmers for one rough opening. Cripples above a header are not in that 4. Add them if the opening needs them. Corners that also start the next wall need an extra stud this count does not see. Board feet of the pile is board feet. Sheathing is plywood. The board on the face is drywall.
FAQ
How many studs?
Wall length divided by spacing, rounded up, plus one stud at the end, plus the extras at each opening. A 16 foot wall at 16 inches on center is 13 studs before openings. One door with two kings and two trimmers adds 4, so 17.
How many plates?
Three rows is a single bottom plate and a double top plate. 3 × 16 feet is 48 linear feet. In 16 foot sticks that is 3 pieces, if the wall is one straight run.
Sources
- NIST Handbook 44: Feet and inches for spacing. The extra studs at an opening are the kings and trimmers you choose to frame.