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What Do Rough Sawn, S2S, S3S, and S4S Mean?

Those letters tell you how much machining the board already has. Rough still needs flattening and thicknessing. S2S is surfaced two sides (the faces). S3S means that plus one straight-line edge — often labeled S2S SL1E (straight-line one edge). S4S is surfaced four sides — closer to dimensional lumber. At Fells Hardwood Supply we sell by the board foot, and most of what we carry is S2S or S2S SL1E. We do not stock much rough lumber; only a few exotics come in rough.

Quick glossary

end view no milled faces

Rough sawn

As from the mill; faces and edges still need work in your shop.

end view 2 faces · edges rough

S2S

Surfaced two sides; thicknessed, but not necessarily true-flat or edged. Expect to joint and plane again for furniture glue-ups.

end view · S2S SL1E 2 faces + 1 edge

S3S

Both faces planed plus one straight-line edge. Tags often say S2S SL1E or SLR1E — same step, so you have a straight reference to rip or glue from.

end view all 4 sides milled

S4S

Surfaced four sides — faces and edges machined, more like dimensional lumber, usually thinner leftover for the same starting quarter.

None of these letters change board-foot math. Pricing still uses nominal rough thickness (4/4 = 1" in the formula). See how hardwood is sold.

Why isn’t my S2S board flat?

Surfacing two faces does not guarantee flatness at all. Wind (twist) is only one kind of warp — a board can also cup, bow, or crook. A thickness planer follows the existing shape; it doesn’t create a true face the way a jointer does. Moisture change after milling can also bring warp back. For tabletops and casework, plan to true faces again before glue-up — that’s normal, not a defect in the label. See bow, cup, crook, and twist.

S2S means two faces were planed; the board can still cup S2S — faces planed smooth faces ≠ flat board Still needs a true face joint first, then plane parallel
A thickness planer follows the board’s existing shape. Joint one face flat before you trust the thickness.

Is S4S always “ready to use”?

It’s closer — but check actual thickness, square, and moisture. Joinery and panels still need careful layout. You’re often paying for milling you could do yourself with a jointer and planer, and you may have less thickness left if something warps after you get home. Handy for trim-style parts and fast builds; less ideal when you need every bit of thickness.

Does surfacing change board-foot math?

No. A 4/4 board planed to 13/16" still counts as 1" thick in the board-foot formula. Dealers price the blank, not the finished caliper reading. That’s industry-wide, not a Fells Hardwood Supply quirk.

Deeper teaching: Thickness and milling terms. Next: Should I buy S4S or S2S? · Bow, cup, crook, twist · All FAQs

Fells Hardwood Supply — Hutto, TX — serving Austin, Round Rock, Cedar Park, Georgetown, and the greater Austin metro.