Board Foot Calculator
A board foot is 144 cubic inches of lumber — one square foot, one inch thick. Enter your dimensions and piece count to get the total, plus what it costs once you allow for waste.
What a board foot actually measures
A board foot is a volume, not a length or an area: 144 cubic inches, which is a piece 12" × 12" × 1".
The formula is thickness × width × length ÷ 144 with everything in inches. If length is in feet, the divisor becomes 12 instead — this calculator handles either.
The reason board feet exist is that hardwood comes in random widths and lengths. You cannot price a stack of walnut by the piece the way you price 2×4s, so mills sell volume.
Nominal versus actual thickness — the expensive mistake
Rough hardwood is sold by its rough thickness, before surfacing. A board sold as 4/4 (one inch) arrives at roughly 13/16" after it has been planed on two faces. You are charged for the inch.
The same trap in softwood is worse. A "2×4" is actually 1.5" × 3.5", so its real board footage is about half what the name implies.
Enter the thickness the seller is charging for, not the thickness you measure after surfacing. For a project you are designing, work backwards: decide the finished thickness you need, then buy the next quarter up.
Quarter sizing
Hardwood thickness is quoted in quarter-inches. 4/4 is one inch, 5/4 is 1.25", 6/4 is 1.5", 8/4 is two inches, 12/4 is three. The calculator shows the notation for whatever you enter so you can check it against a supplier's price list.
Waste allowance
The default is 15%. Rough-sawn hardwood has bark edges, checks, knots, and cup that you cut around, and every crosscut loses a saw kerf.
Ten percent is optimistic and only realistic for select-grade material with straight grain. Twenty to thirty percent is normal for rustic or lower grades, and for projects with lots of short parts where offcuts cannot be reused. If you need specific long clear pieces — a table top, a run of matching stiles — plan higher still, because one defect in the wrong place ruins a whole board.
The "board feet to buy" output is the number to bring to the lumberyard. The plain total is what ends up in the finished piece.
Frequently asked questions
How do you calculate board feet?
Multiply thickness in inches by width in inches by length in inches, then divide by 144. If length is in feet, divide by 12 instead. A board 1" × 6" × 8 feet is (1 × 6 × 96) ÷ 144 = 4 board feet.
Do I use nominal or actual thickness?
Use the thickness the seller charges for, which is the rough thickness before surfacing. Hardwood sold as 4/4 measures about 13/16" after planing but is priced as a full inch. Softwood is worse — a nominal 2×4 is actually 1.5" × 3.5".
What does 4/4 or 8/4 mean?
It is thickness in quarter-inches. 4/4 is one inch, 5/4 is 1.25", 6/4 is 1.5", 8/4 is two inches. Mills quote hardwood this way, and the notation always refers to rough thickness.
What is the difference between a board foot and a linear foot?
A linear foot measures only length and ignores thickness and width, which is how dimensional softwood and trim are usually sold. A board foot measures volume, which is how hardwood is sold because it comes in random widths.
How much waste should I allow?
Ten to twenty percent is typical for rough-sawn hardwood. Go higher — twenty-five to thirty-five percent — for rustic grades, for projects made of many short pieces, or when you need long defect-free runs like a table top or matching door stiles.