Board Foot Calculator

A board foot is a piece of wood 12 inches long, 12 inches wide, and 1 inch thick: 144 cubic inches. To count board feet, multiply the thickness in inches by the width in inches by the length in feet, then divide by 12. If you measured the length in inches, divide by 144 instead.

Use the nominal size, the one on the tag. The USDA Wood Handbook defines board feet for lumber 1 inch or thicker on nominal thickness and width and actual length, and lumber under 1 inch nominal is counted as a full inch. So a 2x4x8 is 2 x 4 x 8 / 12 = 5.33 board feet, even though the stud is really 1-1/2 x 3-1/2 inches.

For a whole order, work out each size, multiply by the number of pieces, and add them up. The calculator does that for a list of up to 30 sizes.

Hardwood lumber yards sell by the board foot, by thickness in quarter inches: 4/4 (“four quarter”) is 1 inch, 8/4 is 2 inches. The boards come in random widths and in lengths from 4 to 16 feet, so you count board feet board by board, or use an average width. The price is for the rough size, even after the yard planes it smooth.

Plan on extra. Rough boards have knots, checks, and wane to cut around, and planing and jointing take material off every face. The calculator starts at 20 percent for rough hardwood and 10 percent for construction lumber. Those are rules of thumb; change them to suit the job.

Home centers price studs and boards per piece; hardwood yards price per board foot; trim and decking are often per linear foot. They are easy to compare once you divide:

• Per board foot = price per piece / board feet in the piece. A 2x4x8 at $4.00 is $0.75 per board foot.
• Per linear foot = price per piece / length in feet. The same 2x4 is $0.50 per linear foot.
• Board feet from linear feet = linear feet x nominal thickness x nominal width / 12. Forty linear feet of 1x6 is 20 board feet.

Those prices are only examples. Switch the ticket to per piece pricing and type in shelf prices, and it shows the board foot and linear foot price for the whole order.

Weight depends on the species and, even more, on how wet the wood is. The calculator works it out the way the Wood Handbook does: specific gravity x 62.4 lb per cubic foot x (1 + moisture content). It uses the actual size of each piece, not the nominal one, because a 2x4 only holds 5.25 square inches of wood, not 8.

“Construction” uses 19 percent, the most that dry studs and boards can hold, so it errs heavy. “Wet or fresh-treated” uses the average moisture of green wood for that species. Pressure-treated lumber can come home still soaked from treatment, and the Wood Handbook notes you can tell because it is exceptionally heavy. That is the load to plan the truck around.

Lumber fails the truck check on weight and length, not bed space. A half-ton pickup with a 1,150 lb payload carries about 104 dry southern pine 2x4x8s, but only about 64 if they are fresh-treated and wet. Check your door-jamb sticker and enter your own payload above.

Then length. Eight-foot boards stick out of a 6.5 ft bed by 1.5 ft; 16 ft boards stick out 9.5 ft. Federal rules for commercial vehicles (49 CFR 393.87) require a red or orange flag at least 18 inches square on any load more than 4 feet past the rear, and many states have a flag rule for every vehicle. Check yours, strap the load at two points, and for long or heavy orders, ask the yard about delivery or a rack.

Building something bigger? The concrete calculator handles the post holes, and the gravel calculator covers the base under a shed or deck.

• Board feet use nominal sizes. A 2x4 is really 1-1/2 x 3-1/2 in, but you pay for 2 x 4. (USDA Forest Products Laboratory)
• Hardwood is sold rough by the quarter: 4/4 is 1 in rough and about 13/16 in once surfaced on both faces. (USDA Forest Products Laboratory)
• Fresh pressure-treated lumber can still be soaked from treatment, and much heavier than dry wood. Let it dry before staining. (USDA Forest Products Laboratory)
• A full bed of dry lumber weighs more than most half-ton payloads, so lumber is a weight check, plus a length check for anything longer than the bed.

• Using actual sizes for board feet. You pay on nominal: 2 x 4, not 1-1/2 x 3-1/2.
• Using nominal sizes for fit. A wall of 2x4s is 3-1/2 inches thick, and three 2x4s laid flat cover 10-1/2 inches, not 12.
• Ordering exact counts. One split board or a bad cut and you are back at the store; add 10 percent.
• Buying rough hardwood by the finished thickness. 4/4 rough planes down to about 13/16 inch.
• Loading a full order of wet treated lumber into a half-ton pickup in one trip.