Hardwood buying guide: 4/4, S2S, rough lumber and grades explained

Thickness: the quarter system

Hardwood thickness is expressed in quarters of an inch of rough-sawn thickness. The number before the slash is the count of quarters:

Rough 4/4 that has cupped or twisted may not flatten out to a full ¾ in. If your plan needs ¾ in parts from warped or long boards, 5/4 gives you margin.

Rough, S2S, S4S and SLR1E

• Rough — straight from the sawmill and kiln. Cheapest per board foot, but you need a jointer and planer (or a patient hand plane) to make it usable. You also get to see the grain and defects only after the first pass.
• S2S (surfaced two sides) — both faces planed; edges still rough. Common at hardwood dealers.
• S2S SL1E / SLR1E — two faces planed and one edge straight-line ripped, so you have one straight edge to run against a table saw fence.
• S4S — all four faces surfaced, ready to use. Most convenient and usually most expensive; common at home centers in narrow widths.

Board feet are normally figured on the rough thickness regardless of surfacing. A surfaced 4/4 board is still tallied at 1 in, so one 8 in wide and 8 ft long comes to 5.33 board feet — see board feet in a 4/4 hardwood board, 8 in × 8 ft. The formula is the same one used for construction lumber, where how many board feet in a 2x6x8 works out to exactly one per foot; the difference is that hardwood uses the rough quarter thickness and the measured width of each board.

Grades

US hardwood grades, set by the National Hardwood Lumber Association (NHLA) and illustrated board by board in the American Hardwood Export Council’s grading guide, describe how much clear, defect-free wood you can cut from a board — not how nice the figure is. Each grade sets a minimum board size and a minimum clear-cutting yield: the share of the board’s surface measure you can cut into clear pieces of at least a set size.

FAS One Face and Selects are separate grades, even though both are FAS on one face and No. 1 Common on the other: Selects simply accepts smaller boards. Dealers often sell FAS, F1F and Selects together as “FAS”, so ask what the mix is if it matters for your parts.

For furniture with long, clear parts, FAS or Select saves time. For projects with many short parts — drawer sides, face frames, small boxes — No. 1 Common is often the better value, because you cut around the knots anyway.

Moisture: kiln-dried vs air-dried

Furniture lumber should be kiln-dried (KD) or air-dried and then acclimated, to roughly the moisture content it will live at indoors — often around 6–9% in heated homes, depending on climate. Wood that is too wet will shrink, check and loosen joints after you build. The USDA Forest Products Laboratory’s Wood Handbook (chapter 4) explains why: wood shrinks and swells as its moisture content follows the humidity around it. A pin moisture meter is inexpensive insurance; check a few boards from the pile.

Once you get the wood home, stack it flat with spacers (stickers) and let it sit in your shop for a week or two before milling, so it settles to your conditions.

How much to buy

1. List every part at its finished size.
2. Convert to rough stock: thickness in quarters (a ¾ in part from 4/4), width plus about ¼–½ in, length plus 1–2 in.
3. Total the board feet by thickness.
4. Add 20–30% for waste — more for Common grades, figured wood, or if you are matching color and grain.
5. At the yard, choose boards to fit your longest and widest parts first.

Checking a pile against the invoice? The hardwood tally calculator tallies a list of boards the way the yard does. Buying by the bundle? A lot of 100 board feet of 4/4 averaging 6 in wide is 200 linear feet of board — 100 board feet of 4/4 × 6 in in linear feet breaks it into boards. For a single wide piece, board feet in an 8/4 slab, 24 in × 8 ft covers measuring a live edge. The board foot chart lists 4/4 to 8/4 per linear foot at common widths.

At the lumberyard

• Bring a cut list, a tape measure and a block plane or a small scraper — dealers usually do not mind you shaving a corner to see the grain, but ask first.
• Restack the pile as you found it. Picking through boards is expected; leaving a mess is not.
• Look for straight grain on parts that need strength (legs, rails) and save wild figure for panels and tops.
• Sight down each board for bow, crook, cup and twist. A little is fine if the part is short; a lot costs you thickness.
• Check ends for checks (cracks) — plan to cut off at least a few inches.
• Ask how the yard tallies. Under the NHLA rules each board’s surface measure is rounded to a whole number and fractions of a foot of length are dropped, so their board footage may differ slightly from yours.

Common species at a glance

Red oak, white oak, hard and soft maple, cherry, walnut, ash and poplar make up most of what US hardwood dealers stock. Poplar is inexpensive and paints well; oak and maple are hard and durable; cherry and walnut are prized for color. Our wood species guide compares hardness, weight and stability.