What Does S4s Mean
Surfaced on all four sides
- S4S = a board planed smooth on both faces and both edges
Methodstandard dimensional lumber (2x4, 2x6, etc.) is sold S4S, which is why its actual size runs under its nominal size.
S4S stock cannot be resawn to true nominal dimensions later — the surfacing loss already happened.
S4S means "surfaced on all four sides" — a board planed smooth on both wide faces and jointed square on both edges, which is why standard dimensional lumber like a 2x4 measures smaller than its nominal name promises.
Why this one specifically
Nearly every piece of construction lumber at a home-improvement store is sold S4S, which is exactly why a "2x4" isn't actually 2" by 4" — the mill starts with a rough-cut board close to the nominal size, then removes roughly 3/4" total from a dimension surfacing all four faces smooth and square, landing at the familiar 1.5" x 3.5" actual size. Hardwood, by contrast, is more often sold rough or S2S specifically so the buyer controls how much material a jointer and planer remove, rather than accepting whatever the mill already took off.
What moves the number
There's no number to move here — S4S describes a milling process, not a dimension. What it does affect is every downstream calculation: board-foot math on S4S dimensional lumber has to use the actual surfaced size, not the nominal name, or the result overstates the true volume by a meaningful margin.