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From Tree to Table · Part 3 of 9

Thickness, Milling Terms, and Board Feet

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Commercial hardwood is sold by rough quarter thickness, how much milling it already has, and volume in board feet. Terms like 4/4, S2S, and S4S tell you what you are buying before you mill to size. Widths and lengths vary. We sell lumber in standard board foot pricing, and we can mill boards to size at a fair rate.

This chapter clears up common confusion at the counter. Someone asks for one-inch walnut and points at an S2S board measuring 13/16". Both of you are right. You are using different terms for thickness. Here is the vocabulary we use at Fells Hardwood Supply, and what to look for on bundle tags in the store.

The quarter system (4/4, 6/4, 8/4, etc.)

Thickness is named in quarters of an inch of rough stock before you joint and plane. Common examples, not a complete catalog:

  • 4/4 is about 1" rough. It typically finishes at 13/16" or 3/4" after milling.
  • 5/4 is about 1¼" rough. It often finishes near 1".
  • 6/4 is about 1½" rough. It often finishes near 1¼".
  • 8/4 is about 2" rough. It often finishes near 1¾".

Dealers also carry other quarters (10/4, 12/4, 16/4, and more) depending on species and pack. Buy starting thickness for the finished size you need, plus allowance for snipe, twist, and a final skim pass. If your parts must finish at a full 1", start at 5/4 or 6/4. Not 4/4.

In the store, thickness is usually sorted in bins or bundles. 4/4 cherry here, 8/4 walnut there. The tag should say the quarter thickness even if the faces are already surfaced.

Widths and lengths vary

Dealer hardwood comes in varying widths and lengths within a pack. It is not one fixed size like a pre-cut 1×6×8. Some bundles are random length and width (RL/RW). Others are width-sorted (“6–8" width cherry”) or width-specified. You are buying board footage to fill a cut list, not a SKU with fixed width and thickness.

Walk the cut list before you pull boards. A project that needs three 8" wide panels may require five boards from the store once you account for defects and grain match.

Milling designations

Rough sawn
Off the mill, fuzzy and uneven. You joint one face, plane to thickness, rip to width. You get the most control and the lowest mill cost.
Skip planed (hit or miss)
Light passes to reveal grain for grading at the mill. Skip planing does not flatten the board. Seeing the grain is not the same as being ready for the table saw.
S2S (surfaced two sides)
Both faces planed to thickness. Edges still rough. Surfacing two faces does not guarantee flatness at all. Cup, bow, crook, and twist can remain or spring back after milling. Face-joint before you trust the thickness.
S3S
Surfaced three sides. S2S plus one straight-line edge. You will often see S2S SL1E (straight-line one edge) on tags instead of “S3S.” That means the same thing.
SLR1E
Straight-line ripped one edge (the SL1E step above). Saves a table-saw fence reference if the board is already flat enough.
S4S (surfaced four sides)
Boards milled on all four faces, often sold by the linear foot. You pay for the milling time and the wood that became shavings.

End views below. Purple and solid edges are milled. Dashed edges are still rough. S2S does not guarantee flatness.

end view · rough faces & edges unfinished

Rough

Nothing surfaced yet. You mill everything in the shop.

end view · S2S 2 faces · not necessarily flat

S2S

Surfaced two sides (the faces). Edges still rough. Planed is not the same as flat.

end view · S3S / S2S SL1E 2 faces + 1 straight edge

S3S (S2S SL1E)

S2S plus one straight-line edge. A rip and glue reference. Still not a flatness guarantee.

end view · S4S all 4 sides milled

S4S

Faces and edges already milled. Ready-to-use stock, usually thinner leftover for the same quarter.

Bring your phone to the store and we will walk a bundle tag together. Species, grade, quarter thickness, surfacing, sort, and tally, one line at a time. Short FAQs: Rough, S2S, S3S, S4S · bow, cup, crook, twist.

Warp: why S2S is not the same as flat

Surfacing two faces does not make a board flat. A thickness planer follows the board’s existing shape. Cup (across the width), bow (along the length on the face), crook (along the length on the edge), and twist or wind (corners not in one plane) are different problems. Wind is only one of them. Full FAQ with jointing order: bow, cup, crook, and twist.

Cup

Faces curve across the width.

Bow

Face curves along the length.

Crook

Edge curves along the length.

Twist / wind

Corners not in one plane.

Joint face, plane parallel, joint edge, rip second edge 1. Joint face 2. Plane parallel 3. Joint edge 4. Rip 2nd edge Hollow face to the jointer bed when you can. Then plane, straighten one edge, rip the other.
Jointing order for a warped board. Detail and waste allowance are in the warp FAQ.

How board feet work

Hardwood is priced by volume in board feet, not by the finished size you will mill to. One board foot is 144 cubic inches of wood. A piece 1" thick × 12" wide × 12" long, measured at nominal rough thickness.

BF = Thickness (in) × Width (in) × Length (in) ÷ 144

Always use the nominal rough thickness in the formula, even if the board is already S2S. A 4/4 board planed to 13/16" still counts as 1" in the math. You are paying for the wood it took to make that blank, including the shavings on the mill floor.

We sell lumber in standard board foot pricing. Widths and lengths vary per board, and if you need specific sizes we can mill boards for you at a fair rate.

Worked example

Suppose you need several parts from 4/4 cherry.

  • Board A: 1" (4/4 nominal) × 6" × 96" → (1 × 6 × 96) ÷ 144 = 4 BF
  • Board B: 1" × 8" × 84" → (1 × 8 × 84) ÷ 144 = 4.67 BF
  • Board C: 1" × 5" × 72" → (1 × 5 × 72) ÷ 144 = 2.5 BF

Subtotal: 11.17 BF before waste. Add 15–30% for planing loss, defects, grain rejects, and miscuts. Use more waste allowance for figured stock or a first big glue-up.

Why nominal thickness matters at checkout

Surfacing removes material, but dealers price the original rough thickness so everyone tallies the same way. If you wonder why you are paying for an inch when the board measures 13/16", look at the quarter tag on the bundle, not the caliper on the surfaced face.

Board feet vs. linear feet

A board foot is volume. That is the standard at hardwood dealers. A linear foot is length of a piece with a fixed width and thickness. Common for S4S moulding and pre-sized boards. Do not convert fixed-size linear-foot thinking into dealer board-foot pricing. The units describe different products.

From cut list to boards

  1. Write finished part sizes (length × width × finished thickness).
  2. Convert each part to board feet at the rough thickness you will buy (4/4, 5/4, etc.).
  3. Sum the parts, then add waste.
  4. Look through the boards with the total in mind and pull extra width for grain match and defect cut-around.

Shorter FAQ versions are How is hardwood lumber sold? and How much wood for my project?

Bring a cut list on paper. We will tally board feet together on a real bundle before you commit. Same math the register uses.

S4S vs. S2S. What we recommend

At Fells Hardwood Supply most boards are S2S or S2S SL1E. Rough is uncommon. Only a few exotics come in that way. If you have a jointer and planer (or access to one), S2S lets you control final thickness and yield. S2S does not guarantee the board is already flat, so plan to joint and plane. If you need pieces milled and ready to use and accept paying for milling plus less leftover thickness, S4S is fine for small parts. Verify actual dimensions. An “S4S 1×4” may not match the nominal sizes you see on construction lumber.

Related FAQs. Should I buy S4S or S2S? · Bow, cup, crook, and twist