What is a board foot?
A board foot (BF) is 144 cubic inches of wood — the standard lumber trade unit. One board foot is a 12-inch × 12-inch × 1-inch-thick piece (or any equivalent: 6×24×1, 4×12×3, 8×18×1, etc.). The board foot formula is:
BF = (Thickness × Width × Length) ÷ 144 (all measurements in inches)
Hardwood is sold by the board foot; softwood is usually sold by linear foot. A "quarter" system is also common in hardwood: 4/4 = 1 inch rough, 5/4 = 1.25 inch, 8/4 = 2 inch, etc.
What this calculator does differently
Most online board foot calculators compute a single piece. The reason that's a problem: when you buy lumber, you don't buy the perfect piece — you buy the rough stock you can find, then trim around defects. That's the waste factor, and it ranges from 10% (clean FAS-grade stock) to 30% (first-time with figured wood, or working with twisted reclaimed lumber).
This calculator lets you pick a waste factor based on your actual conditions, then computes the full pack you'll need to walk out of the lumber yard with.
How to choose a waste factor
- 10% — Use only when you're buying FAS or Select grade from a hardwood dealer, ripping straight pieces, and have done this before.
- 15% (default) — Common-1-Common stock, simple project, straight grain, you know how to read a board.
- 20% — You're matching grain direction on panels, working with mildly figured wood (curly, quartersawn), or buying from a big-box store with inconsistent grading.
- 25% — Reclaimed lumber, twisted boards, or you're still developing board-reading skill.
- 30% — Your first project with crotch wood, burl, or burl-figured maple. Or you have a strict grain-match requirement on multiple faces.
When this calculator is wrong
- If you're building a panel that needs book-matched grain, the waste factor isn't just material waste — you'll need to lay out the cuts from one wide board. Increase to 25-30%.
- If you're buying S4S (surfaced four sides) lumber, the actual dimensions are smaller than nominal. A "4/4" board surfaced to 13/16" is now 6.49 BF per nominal 8 BF, but you're paying for the full 8 BF.
- If your project has long rip cuts, a single bad edge can ruin the entire piece. Plan for an extra piece.
- If you're ordering online, add shipping and a buffer for pieces that arrive with hidden defects.
Cost-per-BF sanity check
Hardwood prices vary wildly by region and grade. As of 2026, rough reference ranges in the US:
- Poplar: $3-5/BF
- Red Oak: $4-7/BF
- Maple (hard): $5-8/BF
- Walnut: $9-15/BF
- Cherry: $7-12/BF
- White Oak (quartersawn): $12-20/BF
If your quote is well below these ranges, the stock is probably Common grade or not properly dried. If it's well above, ask if it's figured or wider-than-average stock.
Frequently asked questions
How do I convert board feet to linear feet?
Linear feet only makes sense for stock of a single fixed width. Formula: Linear Feet = BF × 12 ÷ (Thickness × Width). For mixed sizes, use our Cut List Optimizer.
Do I pay for full board feet even if my piece is smaller?
Yes. If you buy a 6-foot-long, 8-inch-wide, 4/4 board, that's exactly 4 BF and you pay for 4 BF — even if your project only uses 2 BF of it. The waste goes into your scrap pile or your shop.
Should I round up or down at the lumber yard?
Always round up to the next whole board. A board foot is the trade unit, not a precision. If the calculator says 11.4 BF, buy 12 BF worth of stock. Better to come home with an extra short piece than to come up short on the third cut.