How to calculate board feet
Hardwood is sold by volume, not by the piece. A board foot is 144 cubic inches — one inch thick, twelve inches wide, one foot long — and every price a hardwood yard quotes you is per board foot of that volume. The arithmetic is simple; the part that catches people is that all three dimensions have to be in inches before you divide.
- thickness — nominal thickness in inches, the figure the yard prices on, not the planed measurement
- width — the face width in inches
- length — usually quoted in feet, so multiply by twelve before dividing
- 144 — cubic inches in a board foot: 1 × 12 × 12
Worked example: three 2 × 10 boards, twelve feet long
The middle line is worth pausing on. The 144 in the numerator is the length in inches and the 144 in the denominator is the definition of a board foot; they cancel here purely because the board happens to be twelve feet long. Change the length to ten feet and the coincidence disappears.
Why there is no waste allowance on this tool
Every other calculator on this site adds a waste percentage, because the material is uniform and the losses are predictable. Solid timber is not uniform. One board is clear and the next has a knot through the middle of the only length you needed, and the allowance that covers it depends entirely on the grade you bought and the parts you are cutting.
Twenty to thirty percent over the finished volume is the working figure for furniture in a decent grade, and it climbs steeply if you are matching grain across a panel or working around defects in a lower grade. That is a judgement about your boards, not a constant, so this tool gives you the honest volume and leaves the allowance to you.
Common mistakes
- Leaving the length in feet. A twelve-foot board is 144 inches. Divide by 144 without converting first and you get one twelfth of the real figure — the same class of error as leaving slab thickness in inches.
- Using the planed thickness. A 4/4 board planed to 13/16 in is still sold as one inch. Measuring what arrived rather than what was quoted understates the bill by about a fifth.
- Applying board feet to sheet goods. Plywood, MDF and melamine are sold by the sheet, not by volume. Use the cut list optimizer for those.
- Confusing board feet with lineal feet. Lineal feet count length alone and ignore thickness and width entirely. Trim and moulding are sold that way; boards are not.
- Averaging a waney width by eye. On live-edge stock, find out whether your yard measures at the narrowest point or takes an average, because the difference on a wide board is real money.
When these numbers do not apply
- Softwood dimensional lumber. A 2 × 4 is priced per piece or per lineal foot at most yards, and its actual size is 1.5 × 3.5 in. Board feet are the wrong unit for it.
- Rough-sawn stock you intend to surface. You are billed on the rough dimensions, so budget the volume you buy rather than the volume you end up with after planing.
- Timber sold by the cubic metre. Common outside North America. One cubic metre is roughly 424 board feet, but check whether the quote is for sawn or finished volume before converting.
- Veneer and thin stock. Anything under about 3/8 in is usually sold by area or by the sheet, because the board foot becomes an awkward unit at that thickness.