Board feet, S2S, and S4S: the lumber terms every woodworker must understand before buying

The board foot is the universal measure of volume used in hardwood lumber pricing, which is one square foot thick by one inch (length (ft) × width (in) × thickness (in) ÷ 12). S2S is the name of the wood where only two surfaces have been surfaced smooth, and S4S means lumber that has been surfaced and squared on all four sides and is therefore ready for construction right out of the box. Understanding board feet lumber pricing alongside S2S and S4S surfacing before you buy prevents sizing surprises and helps you compare hardwood lumber prices accurately, whether you're pricing 4/4 lumber for a tabletop or 12/4 lumber for a bowl blank.

What Is a Board Foot in Lumber?

Unlike a linear foot, which will measure only the length, a board foot will measure three dimensions, that is, length, width, and thickness. The reason why hardwood is priced by the board foot instead of the running foot is that exotic hardwoods and special lumber differ widely in width and thickness, hence volume is the best means of comparing different boards.

The board foot measurement formula is: board feet = length (ft) × width (in) × thickness (in) ÷ 12. One board foot equals 144 cubic inches, or it’s 1/12 of a cubic foot. Get the formula right, and you can do the price comparison for any species, any size, in seconds, no hassle.

How Do You Calculate Board Feet? (Worked Example)

For example, you need to calculate the price for a 6/4 Walnut board measuring 8' long and 7" wide. Input it in the formula above:

Example Calculation

Length: 8 ft Width: 7 in Thickness: 1.5 in

Board feet = (8 × 7 × 1.5) ÷ 12 = 7 board feet

Multiply by the per-board-foot price to get the total cost of that board.

Do you feel like doing the calculations manually? We provide our Board Feet Calculator entirely for free, allowing you to run any parameters through it and get the board foot amount, as well as the cost for hardwood lumber, turning blanks, or lumber boards of whatever kind.

How do 4/4, 8/4, and 12/4 wood descriptions affect lumber?

Wood thickness is measured in quarter-inches, based on the rough footage of the timber prior to its processing. This measurement is important in comparing different types of wood, as it indicates how thick the piece of wood is to help you understand how much it weighs in terms of different types of lumber.

Keep in mind that surfacing removes material. A rough 4/4 board typically finishes closer to 13/16″ once it's been through the planer so always order rough thickness with that trim allowance in mind.

S2S vs. S4S Lumber – What’s the Difference?

Once a board is milled, it can be left rough or surfaced to varying degrees. This is where S2S and S4S lumber come in and both describe how many faces of the board have been machined smooth and true.

Rough-sawn planks give you the most freedom and usually offer the greatest value on a board foot basis because you are buying wood, not processing time. S4S planks will cost a bit more per board foot, but save shop time because the faces and edges are all planar, parallel, and perpendicular when they arrive.

Common Mistakes When Buying Hardwood Lumber

Avoid These Buying Mistakes

• Confusion about nominal (approximate) thickness versus actual thickness 4/4 stock is actually less than 1 inch thick when surfaced.
• Comparing prices by the board instead of by the board foot, which hides the true cost per unit of wood.
• Buying S2S stock when a project calls for S4S stock projects requiring squared, glued joints require S4S, not S2S.
• Skipping the board feet calculator and estimating by eye, which almost always underestimates material needed for waste and defects.

With just a little pre-planning understanding your board foot measurement, desired thickness in quarters, and S2S vs S4S requirements you can keep your material costs accurate and minimize surfacing time in your shop to focus on construction.

Why Buy Hardwood Lumber From Exotic Wood Zone?

Exotic Wood Zone stocks 4/4, 8/4, and 12/4 hardwood lumber across dozens of domestic and exotic species, cut and surfaced to the specification your project actually needs. Every board is measured and priced by board footage, so what you see is what you pay for no guesswork.

Need something thinner? Our thin dimensional lumber collection covers precise stock for inlay, box-making, and joinery surfaced and ready whenever your build calls for it.

Frequently Asked Questions

1. Is S4S lumber more expensive than S2S lumber?
   Most often, yes, since the price of S4S material is somewhat higher per board foot, since all four sides are milled to be square and flat.

2. What's the difference between a board foot and a linear foot?
   A linear foot measures length only, in one-foot increments. A board foot measures volume length, width, and thickness combined which is why hardwood lumber is priced this way instead.

3. Can I buy rough-sawn lumber and surface it myself?
   Yes, Rough lumber gives you the most flexibility and typically the lowest price per board foot, provided you have a jointer and planer to true it up yourself.

4. Does Exotic Wood Zone sell both S2S and S4S lumber?
   Yes, Exotic Wood Zone offers rough, S2S, and S4S surfacing options across its hardwood lumber and exotic hardwood collections, so you can order stock exactly as ready-to-use as your project requires.

Conclusion

Board feet, S2S, and S4S aren't just industry jargon, they're the three details that determine what you actually receive and what you actually pay when buying hardwood lumber. Use the board foot formula to compare pricing fairly across species and sizes, choose your thickness by the quarter system (4/4, 8/4, 12/4) based on your project's structural needs, and pick S2S or S4S surfacing based on how much shop prep you're willing to do yourself. Ready to put it into practice? Browse Exotic Wood Zone's exotic hardwood lumber collection, run your dimensions through the free board feet calculator, and order lumber boards surfaced exactly the way your next build requires.

Explore the full hardwood lumber collection at Exotic Wood Zone, or read our related guide on Kiln-Dried vs. Air-Dried Lumber: Which Should You Buy? to round out your buying knowledge before your next order.