Lumber Basics
S4S (Surfaced Four Sides)
Lumber planed smooth on all four sides, both faces and both edges, ready for immediate use without additional milling.
In-Depth Explanation
S4S stands for Surfaced Four Sides and describes lumber run through a planer and jointer to produce smooth parallel faces and straight square edges. This is the most fully processed form of surfaced lumber, requiring no additional milling before use. S4S lumber is convenient for DIY builders who lack planing equipment, though it commands a premium over rough-sawn stock. Common variations include S2S (surfaced two sides) and S1S2E (surfaced one side and two edges). When purchasing S4S hardwood, finished dimensions will be smaller than the nominal size due to material removed during planing.
Usage Example
I ordered S4S maple boards so I could go straight to cutting joinery without planing and jointing first.
Related Terms
surfaced-lumber
rough-sawn
actual-size