Length divided by spacing plus one gets you the field studs. Corners, intersections, king and jack studs, and cripples over every opening are the rest — and they are most of the difference.
Height sets the stud length. Precut studs come at 92⅝″ for an 8 ft wall and 104⅝″ for a 9 ft.
Every opening takes two kings, two jacks, and cripples above — and below as well on a window.
Wall length in inches divided by spacing, plus one. That is the number most calculators give you, and on a plain wall with no corners and no openings it would be right.
Real walls have both. Here is what else goes in:
Corners. Conventional detailing uses three studs per outside corner to give backing for drywall on both faces. A two-stud corner with drywall clips does the same job with less wood and leaves room for insulation, which is why it is standard in advanced framing.
Intersections. Where a partition meets this wall, something has to back the drywall and receive the partition. Traditionally a solid stud pack; ladder blocking does it with less lumber.
Openings. Each one takes two king studs full height, two jack studs carrying the header, and cripples above — plus cripples below on a window. That is six or more pieces per opening before the header itself.
Three times the wall length for a conventional wall: one bottom plate and a doubled top plate. Single top plates are permitted in some advanced framing assemblies, but only when the framing above lines up with the studs below, because the second plate is what distributes load that does not land on a stud.
Splices matter. Top plate joints offset from bottom plate joints, and plates lap at every corner and intersection to tie the walls together.
Spreading studs from 16″ to 24″ removes roughly a third of the field studs. The saving in lumber is real, and the insulation benefit is larger than the lumber saving because less of the wall is wood.
But it works as a system, not a single change. Two-stud corners, ladder blocking at intersections, insulated headers, and stack framing so that joists and rafters land over studs. Done piecemeal, most of the benefit disappears and you are left with a wall that flexes more and needs thicker drywall on the ceiling.
Because 92⅝ plus a 1½″ bottom plate and two 1½″ top plates gives 97⅛″ — which puts a 96″ sheet of drywall on with a little clearance top and bottom. The precut length exists to make the sheet goods work.
Not structurally. A flat 2×4 across the opening gives something to nail to, and that is all it is doing.
Ten percent covers crooked stock you reject and cutting loss. Framing lumber is the one material where culling as you go is normal and expected.