The board foot formula
A board foot is a volume: a piece of wood 1 inch thick, 12 inches wide and 1 foot long. Lumber yards that sell hardwood rough, and most sawmills, price everything this way, so it's the number you need before you walk in.
board feet = thickness (in) × width (in) × length (ft) ÷ 12
board feet = thickness (in) × width (in) × length (in) ÷ 144
Say you're buying 8/4 walnut for a table base. One board is 2″ thick, 7″ wide and 8 feet long: 2 × 7 × 8 ÷ 12 = 9.33 board feet. At $14 a board foot that board costs $130.67. Add 15% for waste and you should budget for about 10.7 board feet.
You can list several boards at once. Each line takes a quantity, and the totals at the top add everything up, including waste and cost, by the formulas on the methodology page.
Nominal, rough and surfaced sizes
Board feet are almost always figured on the size the wood was sold at, not the size you end up with.
- Rough hardwood is measured in quarters before planing. 4/4 is 1″, 8/4 is 2″. Widths are random, so the yard measures each board's actual width, usually rounding to the nearest inch.
- Surfaced hardwood (S2S or S4S) is still billed on the rough thickness. Your 4/4 board might measure 13/16″ after planing, but you pay for 1″.
- Softwood dimensional lumber uses nominal sizes. A 2×6 is 1 1/2″ × 5 1/2″, but it's figured as 2 × 6. Most home centers sell it by the piece anyway, so board feet mainly matter for comparing prices.
Enter the size on the yard's tally sheet, not what your calipers read.
Shopping at the yard with a cut list
Rough lumber is easier to buy if you know the total board feet before you go and the longest and widest pieces you need. At the yard:
- Buy boards a few inches longer than your longest part. Ends often have checks (small splits) you'll cut off.
- Wide boards save glue-ups, so pick them for tabletops if the yard has them. Some yards charge more per board foot for extra width, so ask first.
- Number each board with a lumber crayon as you choose it and write the size down. The tally at the counter will match your list.
- Check moisture content. Kiln-dried furniture stock should read about 6 to 8%. Air-dried wood can be much higher, and it will move as it dries.
How much waste to plan for
Waste covers knots, end checks, sapwood you don't want, and the offcuts left between parts. It depends more on the wood than on your skill:
| Project | Typical waste |
|---|---|
| Shelving and shop furniture, common grade | 10–15% |
| Furniture in FAS or select stock | 15–20% |
| Rough #1 common, or matched grain across a piece | 25–35% |
| Figured wood, live-edge slabs | 35% and up |
Pouring resin into a slab? Once you know what the wood costs, the epoxy calculator tells you how much resin it takes to fill the gap.