Board Feet Calculator
Figure out how much lumber you're actually buying. Enter a board's dimensions to get board feet per piece, total board feet for your order, and total cost if you know the price per board foot.
- Board Feet per Piece
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- Total Board Feet
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- Total Cost
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Assumptions
- Nominal sizing uses the standard S4S dressed-size table (e.g. nominal 2" = 1.5" actual, nominal 4" = 3.5" actual), the same table lumber yards use for construction softwood.
- Actual sizing uses your entered dimensions exactly as measured, with no adjustment.
- Rough-sawn hardwood is conventionally measured and sold at its rough (nominal-quarter) thickness before surfacing: enter the quarter-system decimal equivalent (1", 1.25", 1.5", 2") with Actual selected, not a smaller planed thickness.
- This calculates lumber volume only. It does not apply to log-scale rules (Doyle, Scribner, International 1/4-inch) or spray foam coverage, which measure different things entirely.
Sources
- Smith, Walton R. "Simplified Guidelines to Hardwood Lumber Grading." USDA Forest Service, Southeastern Forest Experiment Station, 1967 (reprinted 1989). Explains hardwood grading under the National Hardwood Lumber Association's rules, which set the board-foot measurement convention used here.
- American Softwood Lumber Standard, Voluntary Product Standard PS 20-20 (U.S. Department of Commerce / NIST, 2020): dressed (surfaced) dimension lumber sizes.
Nominal vs actual dimensions
Construction lumber is sold under a nominal name that hasn't matched its real size since mills stopped shipping rough-sawn stock: a "2x4" starts life close to 2" x 4", then shrinks to 1.5" x 3.5" once it's dried and surfaced (planed smooth on all four sides). That's roughly a 30% difference in cross-sectional area, which carries straight through to board feet. Select Nominal here and this calculator applies the standard dressed-size table automatically; select Actual if you've measured the board yourself or you're working with hardwood.
Hardwood and the quarter system
Hardwood is priced and described differently: instead of nominal call-outs like "2x4," thickness is given in quarters of an inch. 4/4 (four-quarter) is 1" thick, 5/4 is 1.25", 6/4 is 1.5", and 8/4 is 2". Unlike softwood, this rough thickness is generally what you're billed for, even though the board arrives slightly thinner after surfacing, so for board-foot purposes, enter the quarter-system number as-is with Actual selected, rather than the thinner finished dimension.
Worked example
A single nominal 2x4, 8 feet long.
Nominal thickness 2" and width 4" resolve to actual dimensions of 1.5" x 3.5". Board feet = (1.5 x 3.5 x 8) / 12 = 3.5 board feet for the one piece.
Frequently asked questions
What formula does this board feet calculator use?
Board feet = (thickness in inches x width in inches x length in feet) / 12. If you enter length in inches instead, the equivalent formula is (thickness x width x length) / 144: this tool handles that conversion for you based on the length unit you pick. Multiply by quantity for a full order.
Can I convert square feet directly to board feet?
Not without knowing thickness: square footage only measures a flat area, while a board foot measures volume. The shortcut is: board feet = thickness in inches x area in square feet. So 10 square feet of 1"-thick actual material is 10 board feet, but the same 10 square feet at 2" thick is 20 board feet.
How is linear footage different from the board feet shown here?
Linear feet only measures length, ignoring width and thickness entirely: a 1x4 and a 1x12 of the same length have identical linear footage but very different board footage. Board feet accounts for the full volume of wood, which is what actually determines how much material (and typically cost) a board represents.
Does this work for both softwood and hardwood lumber?
Yes. For construction softwood, pick Nominal and enter the call-out size (like 2 and 4 for a 2x4): the standard dressed-size table is applied automatically. For hardwood, pick Actual and enter the real thickness, using the quarter-system decimal equivalent (1", 1.25", 1.5", 2") if that's how your stock is described.
Why does it matter whether I choose nominal or actual sizing?
Because the difference is large: roughly 30% less cross-sectional area once a nominally-sized board is dried and surfaced. Using the wrong mode means every board-foot figure, and any cost calculated from it, comes out wrong by that same margin. When in doubt, measure the board with a tape measure and select Actual.
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