If you've ever stood at a hardwood lumber dealer confused about why a board labeled 4/4 by 6 inches isn't actually an inch thick or six inches wide, you're not alone. Hardwood lumber is sold by the board foot, priced by the grade, and described in a shorthand that assumes you already know the rules. This guide breaks it down so your next lumber yard visit goes well.
A board foot is a unit of volume equal to 144 cubic inches, the equivalent of a piece of lumber 1 inch thick, 12 inches wide, and 12 inches long. The formula is simple: thickness (in inches) x width (in inches) x length (in feet), divided by 12. A board that is 1 inch thick, 6 inches wide, and 8 feet long contains 4 board feet. A board that is 2 inches thick, 8 inches wide, and 10 feet long contains 13.3 board feet. Board feet measure volume, not surface area, which is why a thicker board of the same face dimensions costs more.
This is where most newcomers get tripped up. Hardwood thickness is expressed in quarters of an inch. 4/4 (four-quarter) lumber starts at 1 inch rough-sawn and planes down to about 13/16 to 7/8 inch after surfacing. 5/4 (five-quarter) starts at 1.25 inches and finishes around 1 inch. 8/4 (eight-quarter) is nominally 2 inches rough, finishing around 1-3/4 inch. Width and length are measured at actual rough size. A board sold as 6 inches wide is actually closer to 5.75 inches after surfacing on two sides (S2S). When you're calculating board feet for pricing at the lumber yard, use the nominal rough dimensions, not the finished dimensions. But when you're planning joinery and cuts, work from the actual surfaced dimensions.
Hardwood is graded by the National Hardwood Lumber Association (NHLA) based on the percentage of clear, usable wood in a board. Higher grades have fewer knots and defects and command higher prices.
FAS is the top grade. Boards must be at least 6 inches wide and 8 feet long, and yield at least 83% clear cuttings of a minimum size. FAS is what you want for furniture faces, tabletops, and anything where large, clear panels are essential. It's the most expensive grade and worth it for showpiece work.
Select grade (sometimes called FAS-1-Face) allows one face to meet FAS standards while the other face meets lower requirements. This is useful for projects where only one face shows. No. 1 Common yields 66.67% clear cuttings and is the workhorse grade for most projects. Character, shorter clear sections, and the occasional small knot are all acceptable. For cabinet boxes, drawer parts, and secondary surfaces, No. 1 Common is the practical choice at a significantly lower price per board foot.
No. 2 Common yields 50% clear cuttings. It's used for rustic furniture, painted projects (where character doesn't matter), flooring, and any application where short, clear sections are sufficient. If you're building shop fixtures, utility shelving, or anything that will be painted, No. 2 Common can cut your lumber cost in half compared to FAS.
Rough lumber comes straight from the saw. The surfaces are uneven and fuzzy, and the dimensions are close to nominal but not exact. Surfaced lumber has been run through a planer and sometimes a jointer. S2S means surfaced on two sides (the faces); S4S means all four sides have been surfaced. Rough lumber is cheaper per board foot and gives you more control over final thickness, but you need a thickness planer to flatten it. If you're a beginner or don't have a planer, buy S2S or S4S and save yourself the headache. If you have the equipment, buying rough and milling it yourself saves money and lets you get exactly the thickness your project needs.
Always hand-select your boards when buying hardwood in person. Most dealers allow it, and a few minutes of selection makes a big difference. Look along the length of each board for cupping (edges higher than the center), bowing (the board curves end to end), and twist (the board corkscrews). Slight bow can be flattened on a jointer; heavy twist or cupping takes more material to correct and drives up your waste factor. Add 20-25% to your net board foot requirement to account for defects, snipe (the slight planer marks at the ends of boards), and cut-off waste. When in doubt, buy a little more. Returning unused lumber for store credit is common at hardwood dealers, but running short mid-project and finding the same batch is nearly impossible.
