How to Calculate Board Feet
Board feet is the unit the hardwood trade uses for pricing and ordering. Here is how to calculate it, and the three places people get it wrong.
The formula
Board feet = (thickness in inches × width in inches × length in inches × quantity) ÷ 144.
One board foot is a piece 1 inch thick, 12 inches wide and 12 inches long — 144 cubic inches. Length must be in inches, so an 8 foot board is 96 inches.
A worked example: a 1 × 8 board, 8 feet long. That is 1 × 8 × 96 ÷ 144 = 5.33 board feet.
Reading fractional lumber sizes
Hardwood is sold in quarter-inch fractions. 4/4 means 1 inch thick, 5/4 means 1¼ inches, 6/4 means 1½. These are nominal rough-sawn sizes. A 4/4 board milled for a project comes out about 13/16 inch, sometimes ¾ — but it is still sold and billed as 4/4.
This means: when converting rough lumber to board feet, use the nominal thickness. When you need the actual finished dimensions for a fit calculation, use the milled size. Using the wrong one is how a project ends up with a top that is 1/4 inch too thick.
Where people get it wrong
- Using feet for length. The formula needs inches. An 8 foot board is 96, not 8. Using 8 gives you an answer 12 times too small.
- Forgetting quantity. The formula multiplies by how many boards.
- Adding waste before converting. Convert to board feet first, then add the waste percentage. Adding it to linear feet before the conversion gives a different (wrong) number.
- Mixing up bd ft and solid ft. A board foot is a volume, not a length. Ten board feet of 1 × 12 stock is only 10 linear feet, but the same 10 bd ft in 1 × 6 is 20 linear feet.
Choosing a waste factor
| Project | Waste | Why |
|---|---|---|
| Simple trim, 1–2 cuts per board | 10% | Occasional defects, saw kerf loss |
| Joinery, furniture parts | 15–20% | Many cuts, need matching grain, defects matter |
| Figured or highly clear stock | 25–30% | You are selecting for appearance, so you reject boards |
| Dimension lumber by the piece | 5–10% | Stock is graded and uniform |
Waste factor is about selection, not about the saw. It covers boards you reject because of knots, sapwood, or grain that does not match — plus the material lost to each cut.
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