Board foot calculator
Hardwood is sold by volume, not by the piece, and the unit is the board foot: 144 cubic inches. The formula is simple, but the unit mismatch — inches for thickness and width, feet for length — is where people go wrong.
Your lumber
How this is calculated
Board feet = (thickness in inches × width in inches × length in feet) ÷ 12.
The divisor is 12, not 144, and that trips people up. A board foot is 144 cubic inches — 1″ × 12″ × 12″. Because the length is already in feet, one factor of 12 is already accounted for, so only 12 remains. If you enter everything in inches, you divide by 144 instead.
Worked example
Five boards of 4/4 walnut, 6″ wide, 8 ft long:
- Per board = (1 × 6 × 8) ÷ 12 = 4 bf
- Five boards = 20 bf
- At $9.50/bf = $190
Board feet and cut lists are not the same thing
Board feet measure the volume of wood you bought. They do not tell you how much usable material you have. A 20 bf stack of random-width boards may not yield the parts on your cut list, because widths, lengths, defects and grain direction all constrain what you can actually cut. Plan for 15–25% more board feet than your finished parts measure, and lay out the cuts before you buy.
What this calculator will not apply
- It does not apply NHLA grading or rounding rules. Commercial hardwood tallies use their own conventions for random widths and lengths. A yard's invoice may differ from this arithmetic.
- It does not account for surfacing. Rough 4/4 becomes about 13/16″ after planing. You pay on the rough dimension.
- It does not price your yard. Hardwood pricing varies by species, grade and region far more than softwood does.
Questions people actually ask
How do you calculate board feet?
Thickness in inches × width in inches × length in feet, divided by 12. A 1″ × 6″ × 8 ft board is (1 × 6 × 8) ÷ 12 = 4 board feet.
Why divide by 12 and not 144?
Because length is in feet while thickness and width are in inches. The 12 in the denominator converts feet to inches, leaving 144 cubic inches per board foot accounted for. If you enter length in inches, divide by 144.
How many board feet in a 2×6×8?
(2 × 6 × 8) ÷ 12 = 8 board feet. Note this uses nominal dimensions — the actual 1.5″ × 5.5″ board contains about 5.5 bf of wood.
What does 4/4 mean?
Four quarters of an inch, so 1 inch nominal. 8/4 is 2 inches. Hardwood thickness is quoted in quarters because it is milled from rough stock, and you pay on the nominal quarter.
Should I add waste to board feet?
Yes, if you are buying for a cut list. 15–25% is typical, more for figured wood or when grain matching matters. Board feet measure volume, not yield.