The board-foot formula
For a rectangular board, use thickness and width in inches and length in feet:
If all three dimensions are in inches, divide their product by 144 instead. One board foot equals 144 cubic inches, one-twelfth of a cubic foot, or 0.002359737216 cubic metres.
Worked example: a small shelf project
Suppose your material list contains four boards, each 1 inch thick, 6 inches wide, and 8 feet long. Each board contains 1 × 6 × 8 ÷ 12 = 4 BF. Four matching boards give 16 BF.
Using an example 10% extra allowance gives 16 × 1.10 = 17.6 BF. At an example price of $6.50 per BF, the budget is $114.40 before tax, delivery, and milling. This arithmetic budgets volume; it does not establish whether your required cuts fit those four boards.
Use the board foot calculator to tally different board sizes and compare the measured volume with an allowance-adjusted cost.
Rough, nominal, and finished sizes
The measurements you enter determine what the answer means. An actual-volume calculation uses the thickness and width you measure. A purchase estimate should follow the dimensions and tally convention used by the seller.
A nominal 2 × 4 × 8 board calculates to 5.33 BF when using the labelled 2-inch thickness and 4-inch width. A board measuring 1.5 inches by 3.5 inches by 8 feet contains 3.5 BF of geometric volume. Neither answer is automatically the supplier’s billing quantity.
Everyday Calc Lab uses the dimensions you type. It does not round a 3/4-inch thickness up to 1 inch, round surface measure, or apply NHLA grading rules. Confirm the seller’s tally practice before comparing an invoice with this estimate.
What does 4/4 or 8/4 mean?
Hardwood thickness is often described in quarters of an inch. A 4/4 label corresponds to one inch of nominal rough thickness; 8/4 corresponds to two inches. Surfacing removes material, so a finished board may be thinner. These are thickness labels, not quality grades.
| Label | Nominal rough thickness | Millimetres |
|---|---|---|
| 4/4 | 1 inch | 25.4 |
| 5/4 | 1.25 inches | 31.75 |
| 6/4 | 1.5 inches | 38.1 |
| 8/4 | 2 inches | 50.8 |
| 12/4 | 3 inches | 76.2 |
Board feet, linear feet, and square feet
A linear foot is a length. A square foot is an area. A board foot is a volume. The unit on your price sheet determines which measurements you need.
| Price basis | What you measure | Calculation |
|---|---|---|
| Per board foot | Thickness, width, length | Thickness (in) × width (in) × length (ft) ÷ 12 per board |
| Per linear foot | Required length or area and covering width | Area (sq ft) × 12 ÷ usable width (in) |
| Per square foot | Surface area | Width × length in feet |
Plan your allowance deliberately
Material disappears through trimming, saw kerf, milling, and removing defects. Grain matching can make otherwise usable wood unsuitable for a visible part. Those losses depend on your boards and project, so treat a percentage as a budget assumption you control.
Our allowance means extra material added to the net volume: net × (1 + percentage ÷ 100). It is different from a yield-loss calculation. If 10% of purchased material is unusable, the purchase quantity needed to deliver 16 BF is 16 ÷ 0.90, or about 17.78 BF. Choose the model that matches your estimate.
A quick check before ordering
- Match each dimension to the correct unit. An 8-foot length entered as 96 feet creates a twelvefold error.
- Confirm whether the seller’s price applies to rough stock, surfaced stock, nominal sizes, or a specific tally rule.
- Check every required cut against available stock lengths, widths, defects, and grain direction.
- Use a current supplier quote for pricing. Our default price is only an example.
- Keep your tally and assumptions with the project. Download or print the calculation so you can check changes at the yard.
References and method
The volume formula and definitions were checked against the resources below. Our worked examples are independently calculated, and our tools do not claim certification by these organizations.
- Wood-Mizer: What is a board foot?
- Penn State Extension: Valuing Standing Timber, board-feet section
- Penn State Extension: nominal and actual lumber dimensions
- Hardwood Industries: an example of supplier-specific tally conventions
Found a calculation issue? Send the inputs and expected result so we can investigate.