Updated July 18, 2026
The numbers this calculator uses
This tool runs one line of math: thickness in inches, times width in inches, times length in feet, divided by 12. That single divide-by-12 stands in for the textbook definition of a board foot, 144 cubic inches, because length here is entered in feet rather than inches. Convert length to inches yourself and you would divide by 144 instead, same answer either way.
| Quarter call | Rough thickness |
|---|---|
| 4/4 | 1 in |
| 5/4 | 1-1/4 in |
| 6/4 | 1-1/2 in |
| 8/4 | 2 in |
Hardwood dealers quote thickness in quarters of an inch, so a board sold as 8/4 is 2 inches rough before anyone runs a planer over it. Type whatever thickness your supplier quotes into the calculator above, nominal or actual, and it will treat that number as fact.
| Nominal call | Actual size |
|---|---|
| 2x4 | 1.5 in x 3.5 in |
| 2x6 | 1.5 in x 5.5 in |
| 2x8 | 1.5 in x 7.25 in |
| 2x10 | 1.5 in x 9.25 in |
| 2x12 | 1.5 in x 11.25 in |
The nominal-to-actual table is reference only. The calculator itself does not look up or convert these figures. It multiplies exactly whatever thickness and width you type in, so if your yard sells surfaced framing lumber, enter the actual planed size for a true board-foot count, or the nominal call if you are matching how the invoice will read.
How it works
A board foot is a unit of lumber volume equal to 144 cubic inches: a piece 1 inch thick, 12 inches wide and 12 inches long. The formula is thickness (in) times width (in) times length (ft), divided by 12.
The board-foot formula itself is a fixed unit definition; the buying-overage guidance further down is Inch Calculator's own recommendation, not ours.
Worked examples
Run the formula, thickness times width times length in feet, divided by 12. A 2 inch by 6 inch board that is 8 feet long is (2 x 6 x 8) divided by 12, which is 8 board feet. A nominal 2x4 at 8 feet is (2 x 4 x 8) divided by 12, about 5.33 board feet. A 1 inch by 12 inch shelf board 10 feet long is (1 x 12 x 10) divided by 12, which is exactly 10 board feet. Multiply by the number of boards for the project total, then by your price per board foot to estimate cost.
What a board foot actually is
One board foot is 144 cubic inches, or 1/12 of a cubic foot. It measures volume, not surface area, which is why a thin wide board and a thick narrow one can come out to the same board footage. Hardwood dealers price by the board foot precisely because it makes different sizes comparable.
Buying tips
Buy 15 to 20 percent more board footage than your cut list shows. Defects, snipe, checking at the ends and the simple fact that real boards do not yield perfect cuts all eat into usable wood, and hardwood comes in random widths and lengths rather than tidy sizes. Sticker and acclimate the lumber in the space before you build so it does not move on you afterward. If you are buying surfaced softwood by the piece, the calculator still helps you compare a per-piece price against a per-board-foot quote.
Source: Inch Calculator board footage reference.