Board Foot Calculator
This board foot calculator finds how many board feet are in a piece of lumber from its thickness, width, and length. Enter the board size and quantity to get total board feet, and add a price per board foot for an instant lumber cost.
Quick answer
A board foot is 144 cubic inches of wood, the same as a board 1 inch thick by 12 inches wide by 12 inches long.
What this tells you
- •A board foot is 144 cubic inches of wood, the same as a board 1 inch thick by 12 inches wide by 12 inches long.
- •With length in feet, board feet equal thickness times width times length, divided by 12.
- •Board feet use the nominal size you are charged for, not always the finished dimensions.
- •Use the dimensions on the supplier's tally because rough, surfaced, and construction lumber may be measured differently.
- •Add waste separately for defects, end checks, grain selection, milling, and cutting losses.
How to Use
- 1Enter board thickness and width in inches.
- 2Enter board length in feet.
- 3Set the quantity of identical boards.
- 4Optionally enter your price per board foot.
- 5Calculate for total board feet and cost.
How It Works
Formula
Board Feet (one board) = Thickness(in) x Width(in) x Length(ft) / 12
Total Board Feet = Board Feet x Quantity
Cost = Total Board Feet x Price per Board FootBecause a board foot equals 144 cubic inches and a foot of length is 12 inches, the calculation reduces to thickness times width in inches times length in feet, divided by 12.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
How many board feet in a 2x6x8?
Twelve 1x8x10 boards at $4.50 per bf
Ordering 8/4 white oak for a 36 by 72 inch tabletop
Dana is building a dining table with a 36 by 72 inch top and wants 8/4 white oak so it can finish thick. Hardwood is sold by quarters of an inch of thickness, so 8/4 means 2 inches in the rough. The yard has 8/4 boards 7 inches wide and 8 feet long at $7.25 per board foot. Each board is 2 x 7 x 8 / 12 = 9.33 board feet, six boards total 56.00 board feet, and the material comes to $406.00. Six 7-inch boards give 42 inches of width for a 36-inch top, which leaves 6 inches for jointing the edges straight and cutting around sapwood or knots, and 8 feet of length leaves 2 feet to trim end checks from a 72-inch top. Flattening and planing 8/4 stock usually brings it to about 1 3/4 inches, so the top will not finish at a full 2 inches.
Nominal vs actual softwood sizes and board feet per linear foot
Dry dressed sizes for common dimension lumber beside the nominal size it is sold under, with board feet figured on the nominal size, which is how softwood is tallied and priced.
| Nominal size | Actual dressed size, dry | Board feet per linear foot | Board feet in an 8 ft piece |
|---|---|---|---|
| 1x4 | 3/4 x 3 1/2 in | 0.33 | 2.67 |
| 1x6 | 3/4 x 5 1/2 in | 0.50 | 4.00 |
| 1x8 | 3/4 x 7 1/4 in | 0.67 | 5.33 |
| 1x12 | 3/4 x 11 1/4 in | 1.00 | 8.00 |
| 2x4 | 1 1/2 x 3 1/2 in | 0.67 | 5.33 |
| 2x6 | 1 1/2 x 5 1/2 in | 1.00 | 8.00 |
| 2x8 | 1 1/2 x 7 1/4 in | 1.33 | 10.67 |
| 2x10 | 1 1/2 x 9 1/4 in | 1.67 | 13.33 |
| 2x12 | 1 1/2 x 11 1/4 in | 2.00 | 16.00 |
| 4x4 | 3 1/2 x 3 1/2 in | 1.33 | 10.67 |
Dressed sizes are the minimum dry sizes in Voluntary Product Standard PS 20, the American Softwood Lumber Standard. Board feet are computed with the formula above on nominal thickness and width: a board foot is 144 cubic inches, so nominal thickness x nominal width / 12 gives board feet per linear foot, and the 8-foot column uses the same formula with a length of 8 feet. The calculator uses whatever dimensions you enter, so enter nominal sizes to match a lumberyard tally.
What Is a Board Foot?
A board foot is the standard unit for buying and pricing rough lumber, especially hardwood. One board foot is 144 cubic inches, which you can picture as a board 1 inch thick, 12 inches wide, and 12 inches long. It measures volume, so a thicker or wider board holds more board feet per running foot.
Hardwood thickness is often quoted in quarters, where 4/4 means 1 inch and 8/4 means 2 inches. Softwood from the home center is usually sold by the piece at nominal sizes, but the board foot is still how you compare value across thicknesses and species.
Nominal and actual sizes are different numbers by design. Voluntary Product Standard PS 20, the American Softwood Lumber Standard, sets the minimum dressed sizes for dimension lumber: a dry 2x4 is 1 1/2 by 3 1/2 inches, a dry 2x6 is 1 1/2 by 5 1/2 inches, and a dry 1x12 is 3/4 by 11 1/4 inches, where dry means a moisture content of 19 percent or less. The nominal size is the name the board is sold under, left over from the rough-sawn size before drying and surfacing. Home centers sell dimension lumber by the piece, but when softwood is tallied in board feet the count uses the nominal size, so a 2x4 counts 0.67 board feet per linear foot even though its dressed volume is only 1.5 x 3.5 / 12 = 0.44. This calculator multiplies whatever you enter and does not convert between the two, so enter nominal dimensions to match a lumberyard tally and actual dimensions to measure wood you already own.
For random-width hardwood, calculate each board from the thickness, measured width, and length used on the invoice, then add the pieces. Entering one average width and a quantity is only accurate when the boards truly share that width and length. Compare the calculator total with the yard's tally before using it to challenge a quote.
Price per board foot may not be the whole invoice. A supplier can add surfacing, straight-line ripping, milling, delivery, minimum-order charges, taxes, or premiums for wide and long stock. Enter the quoted base rate here for a material subtotal, then add those charges separately. Confirm whether the listed price applies to the species, grade, thickness, and quantity you need.
Board feet measure volume, not coverage or structural capacity. Flooring coverage depends on finished face width and installation waste. Decking, framing, and sheet goods are often estimated by pieces, linear feet, square feet, or sheets. Structural lumber selection also depends on species, grade, span, loading, moisture, and local requirements, none of which this volume calculation checks.
Three things the formula leaves out, and what the sources say about each. Waste: a cutting plan is the best guide, but as a rule of thumb woodworkers add 10 to 20 percent to the finished-part volume for saw kerf, jointing, planing, defects, and grain matching, and more for wide, clear, or color-matched parts. Shrinkage: the Wood Handbook (USDA Forest Service, Forest Products Laboratory, FPL-GTR-190, 2010) tabulates shrinkage from green to oven-dry by species, with tangential values of roughly 8 to 11 percent for oak and hard maple, so a board tallied at its green size arrives thinner and narrower after kiln drying. PS 20 builds the same effect into softwood sizes by listing a green 2x4 at 1 9/16 by 3 9/16 inches and a dry one at 1 1/2 by 3 1/2 inches. Nominal versus actual: the tool cannot tell which you entered, so compare its total with the yard's tally method before treating a difference as an arithmetic error.
Common mistakes
- Entering length in inches instead of feet
- Confusing board feet with linear feet
- Using finished dimensions when you are charged for the nominal size
- Forgetting to set the quantity for multiple boards
- Assuming every supplier tallies nominal and dressed stock in the same way
- Using board feet as square-foot coverage without accounting for finished thickness and width
- Ordering the exact finished-part volume with no allowance for kerf, defects, or milling
- Comparing prices without checking species, grade, thickness, width premiums, and service charges
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