How to calculate board feet in Excel

The board foot formula

One board foot is a piece 1 inch thick, 12 inches wide and 12 inches long: 144 cubic inches. So multiply the three sizes in inches and divide by 144. That's the formula in column G, filled down the cut list.

If your lengths are in feet, multiply thickness x width x length in feet and divide by 12. It's the same number: 1 x 6 x 6 ft / 12 = 3. Pick one unit for the whole sheet and put it in the header ("Length in"), because a mix of inches and feet in one column is the most common way to be off by 12 times.

Total board feet for the cut list

Each row is one part with a quantity, so the total is board feet each x quantity, added up. SUMPRODUCT does that in one cell. The whole project needs 34.74 board feet.

SUMIFS(G2:G7,B2:B7,"Walnut") is a common slip: it adds board feet per part and ignores the Qty column, giving 5.5 instead of 20. To total one species, multiply by the test inside SUMPRODUCT: =SUMPRODUCT(G2:G7*F2:F7*(B2:B7="Walnut")). Write it with * like that. If you pass the test as its own argument, =SUMPRODUCT(G2:G7,F2:F7,B2:B7="Walnut") returns 0, because SUMPRODUCT treats TRUE and FALSE as 0 in that form. Add -- in front of the test to fix it.

Thickness: 4/4, 8/4 and finished vs rough

Hardwood is sold rough by the quarter inch: 4/4 ("four quarter") is 1 inch, 5/4 is 1.25, 8/4 is 2. Board feet use that rough thickness, not what's left after planing. The shelf slats finish at 3/4 inch but you buy 4/4 stock, so row 6 uses 1. Entering 0.75 would show 1.06 board feet per slat instead of 1.41, and you'd come home short.

If your list has thickness written as "8/4", convert it with LEFT and FIND: take the number before the slash and divide by 4.

Softwood dimension lumber is usually figured on nominal size. A 2x4 is really about 1.5 x 3.5 inches, but an 8-foot 2x4 is counted as 2 x 4 x 8 / 12 = 5.33 board feet, not 3.5. Most yards sell those by the piece or linear foot anyway, so ask how your yard prices.

Add waste and round up to what you'll buy

Boards have checks at the ends, knots, defects and saw kerf, and the widths rarely match your parts. Put your waste allowance in an input cell (M2). 20% is only an example; people use more for knotty or rough stock and less for clear, straight boards.

Multiply by (1 + waste), then ROUNDUP to a whole board foot: 34.74 x 1.2 = 41.68, so plan for 42. Round up per species, since you buy each one separately: walnut 20 becomes 24, maple 4.03 becomes 5, red oak 10.71 becomes 13.

Cost per board foot by species

Keep prices in a small table (species and price per board foot), then let SUMPRODUCT look up each row's price. XLOOKUP with a whole column of species returns one price per row (Excel 365 and 2021). In older Excel, SUMIF(I2:I4,B2:B7,J2:J4) does the same lookup.

The parts cost $373.81 at these prices before waste, about $448.57 with 20% added. For a shopping list per species, multiply the rounded-up board feet by the price: 24 walnut board feet at $13.75 is $330. Prices are examples; type in what your yard charges.