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RecommendedWhat a Board Foot Is
A board foot is a unit of volume, not area or length. One board foot equals 144 cubic inches of lumber. The easiest way to picture it is a piece 1 inch thick, 12 inches wide and 12 inches long.
Because it measures volume, the same board foot can take many shapes. A piece 1 inch by 6 inches by 24 inches is one board foot. So is a piece 2 inches by 6 inches by 12 inches, and a piece 1/2 inch by 12 inches by 24 inches. All three contain 144 cubic inches of wood.
This is why hardwood dealers quote a single price per board foot across widths and lengths. A wide board and a narrow one cost the same per unit of wood, which puts every piece on the pile on an equal footing.
Board foot formulaBoard feet = thickness in inches multiplied by width in inches multiplied by length in feet, divided by 12
If the length is in inches instead of feet, divide by 144 rather than 12. Both forms give the same answer, since a board foot is 144 cubic inches.
A Worked Example
A woodworker needs three pieces of 8/4 black walnut, each 7 inches wide and 8 feet long, for a table leg blank set.
- Thickness: 8/4 is 2 inches.
- Width: 7 inches.
- Length: 8 feet.
- Board feet per piece: (2 x 7 x 8) divided by 12 = 112 divided by 12 = 9.33 board feet.
- Three pieces: 9.33 x 3 = 28 board feet.
- At 14 dollars per board foot: 28 x 14 = 392 dollars.
The same calculation in inches: 2 x 7 x 96 = 1,344 cubic inches, divided by 144 = 9.33 board feet. Identical result.
Quarter Measure Thickness
Hardwood is sold in quarter measure, a notation that expresses thickness in quarters of an inch. It is spoken as "four quarter" and "eight quarter", never as a fraction.
Quarter MeasureNominal ThicknessTypical Surfaced Thickness (S2S)
4/41 inch13/16 inch
5/41.25 inch1 1/16 inch
6/41.5 inch1 5/16 inch
8/42 inch1 3/4 inch
10/42.5 inch2 1/4 inch
12/43 inch2 3/4 inch
16/44 inch3 3/4 inch
The key detail is that the board foot calculation for hardwood uses the rough nominal thickness, not the surfaced thickness. Buying 4/4 cherry that has been surfaced to 13/16 inch still bills at 1 inch. That is not a trick. The mill grew, dried and milled a full inch of wood, and the material removed in planing is real cost. Rough sawn stock, sold exactly as it came off the saw, is measured the same way and is often the better buy for anyone with a planer, since the buyer controls how much thickness is left.
Width is treated the same way on rough stock. Most yards measure rough board width to the nearest inch, rounding down on partial inches, and measure length to the nearest foot. A rough board 6 3/8 inches wide and 8 feet 5 inches long is normally tallied as 6 inches by 8 feet.
Rough Sawn Versus Surfaced
- Rough sawn (RGH). Straight off the mill, no planing. Rough surfaces, uneven thickness, but full dimension and the lowest price per board foot.
- S2S. Surfaced two sides, planed to a consistent thickness with the edges still rough. The most common way hardwood is sold at retail.
- S3S. Surfaced two sides plus one straight line ripped edge, giving a reference edge for the table saw.
- S4S. Surfaced four sides, square and ready to use, at the highest price per board foot and the least flexibility.
Plan for 15 to 20 percent extra on a hardwood order for defects, snipe, checked ends and the width lost to jointing. Figured and highly character graded material can run 30 percent or more waste.
Nominal Versus Actual Dimensions
Construction softwood carries a different problem. A 2x4 has not measured 2 inches by 4 inches since the standardization of dressed lumber sizes. The nominal name refers to the rough green size before drying and surfacing.
Nominal SizeActual ThicknessActual WidthBoard Feet per 8 ft Piece
1x40.75 in3.5 in2.67
1x60.75 in5.5 in4.00
2x41.5 in3.5 in5.33
2x61.5 in5.5 in8.00
2x81.5 in7.25 in10.67
2x101.5 in9.25 in13.33
2x121.5 in11.25 in16.00
4x43.5 in3.5 in10.67
Note the pattern break. Boards up to 6 inches nominal lose 1/2 inch of width, but 8 inch and wider lose 3/4 inch, which is why a 2x8 is 7 1/4 and not 7 1/2. The board foot column above uses the nominal dimensions, which is the industry convention when construction lumber is tallied by the board foot, for example on a large framing package or a truckload quote.
Why Hardwood Is Sold by the Board Foot
Hardwood comes off the log in random widths and lengths. A walnut log yields boards from 4 inches to 16 inches wide with live edges, taper and defect, and it would be impractical to stock and price every combination. Pricing by volume means the yard quotes one number per species and grade, and the buyer picks whatever boards suit the project.
Construction softwood is the opposite. It is milled to a small set of standard dimensions in standard lengths, graded to a structural standard, and stacked in identical units. When every 2x4x8 is interchangeable, a per piece price is simpler for everyone, so lumber yards quote it that way at retail. Board foot pricing on softwood shows up mainly in wholesale, in mill quotes and in the thousand board foot (MBF) pricing used across the commodity market.
Calculating Cost
Order costTotal cost = total board feet multiplied by the price per board foot
Then add waste. Multiply the finished board footage of the project by 1.15 to 1.25 before pricing, since offcuts, defects and jointing losses are real material that has to be paid for.
Worked cost example: a project needs 22 board feet of finished 4/4 hard maple. Adding 20 percent for waste gives 26.4 board feet, so 27 board feet is ordered. At 9 dollars per board foot, that is 243 dollars. If the same wood is bought S4S at 13 dollars, the bill is 351 dollars, and the buyer has less thickness to work with because the mill already took some.
Watch for minimum charges and per board minimums. Many yards round each board up to the next whole board foot, and some apply a surcharge for widths over 12 inches or lengths over 12 feet. Kiln dried, select grade and FAS material all carry premiums over common grades. FAS (Firsts and Seconds) is the top National Hardwood Lumber Association grade and yields the largest clear cuttings, while Number 1 Common yields smaller clear pieces at a much lower price and is usually the smarter buy for cabinet parts and small components.
Measure rough boards before they are planedBoard foot billing is based on rough thickness and rough width. If a board is planed or jointed before it is tallied, the buyer loses volume that was already paid for. Tally the pile at the yard, write the numbers down, and check them against the invoice.
Weight and Moisture Content
Board feet tell how much wood is in an order, but not how heavy it will be or how it will behave. Weight depends on species and on moisture content.
- At a normal 6 to 8 percent kiln dried moisture content, red oak and hard maple run roughly 3.5 to 3.8 pounds per board foot.
- Black walnut runs about 3.2 pounds per board foot, cherry about 2.9, poplar about 2.5, and eastern white pine about 2.1.
- Green or air dried lumber can weigh 50 to 100 percent more than the same species kiln dried, because water is still in the cells.
A 100 board foot order of kiln dried red oak weighs around 370 pounds, which is a two person lift in stages and a real consideration for a half ton pickup with other cargo already in the bed.
Moisture content matters even more for stability. Interior furniture and cabinetry needs lumber at 6 to 8 percent. Exterior work is normally built at 12 to 15 percent. Wood bought at the wrong moisture content will move after it is milled, opening joints and cupping panels. Sticker the boards in the shop for one to two weeks before milling so they reach equilibrium with the space they will live in, and calculate board feet on what is actually needed rather than buying more than can be stored properly.