Board Foot Calculator
Add up board feet for a lumber order and estimate the cost. Enter several boards at once, imperial or metric, with the formula and real examples explained.
How to use the board foot calculator
- Enter thickness and width in inches, length in feet, and how many identical boards.
- Add another board for each different size in your cut list.
- Optional: enter a price per board foot to estimate the cost.
- Read total board feet — the number the lumberyard prices on.
The board foot formula, and why it exists
A board foot equals 144 cubic inches of wood — think of a plank 12 inches square and 1 inch thick. The formula is thickness (in) × width (in) × length (ft) ÷ 12. Because it measures volume, it lets you compare a wide thin board with a narrow thick one on equal terms, which is why hardwood dealers price by the board foot rather than by the piece.
| Board | Board feet each |
|---|---|
| 1 × 4 × 8 ft | 2.67 |
| 1 × 6 × 8 ft | 4.00 |
| 2 × 6 × 8 ft | 8.00 |
| 8/4 (2 in) × 10 × 6 ft | 10.00 |
Nominal vs. actual dimensions
This trips up a lot of first orders. A softwood "2 by 4" actually measures about 1.5 by 3.5 inches after surfacing, so its true board-foot volume is smaller than the nominal name suggests. Hardwood sold rough is closer to its stated size. Measure what you are actually paying for — and if the yard quotes nominal, calculate nominal.
The quarter system
Hardwood thickness is written in quarter-inches: 4/4 is 1 inch, 5/4 is 1.25 inches, 6/4 is 1.5 inches, and 8/4 is 2 inches. Thicker stock costs proportionally more per board foot, so a project in 8/4 walnut carries roughly double the material cost of the same faces in 4/4.
Buy a little extra
Real boards have knots, checks, splits and wane. Add 10 to 20 percent to your calculated board feet so you can cut around defects and recover from the occasional bad cut — more for figured, reclaimed or narrow stock.
Frequently asked questions
How do you calculate board feet?
A board foot is thickness in inches times width in inches times length in feet, divided by 12. A 1 by 6 board 8 feet long is 1 × 6 × 8 ÷ 12 = 4 board feet. Multiply by the number of identical boards, and add up different sizes for a total.
What is a board foot?
A board foot is a unit of lumber volume equal to 144 cubic inches — a piece 12 inches square and 1 inch thick, or any shape with the same volume. Hardwood is almost always priced per board foot, so it lets you compare boards of different sizes fairly.
Should I use nominal or actual dimensions?
For rough or surfaced hardwood sold by the board foot, measure the actual size. For softwood framing sold by nominal size, remember a "2 by 4" is really about 1.5 by 3.5 inches; use the nominal figures only if that is how it is being priced.
What do 4/4 and 8/4 mean?
They describe rough thickness in quarter-inches. 4/4 (four-quarter) is 1 inch, 5/4 is 1.25 inches, and 8/4 is 2 inches. Hardwood is ordered in these thicknesses and priced per board foot, so 8/4 stock costs about twice as much per square foot of face as 4/4.
How do I estimate lumber cost from board feet?
Multiply total board feet by the price per board foot. Enter a rate in the optional field and this calculator returns the cost. Buy 10 to 20 percent extra for defects, trimming and mistakes, especially with figured or reclaimed wood.
Board-foot totals and cost estimates are for planning only. Always confirm dimensions, grade and pricing with your lumber supplier, and buy extra to cover defects and cutting.