This board foot calculator converts lumber dimensions into board feet — the standard unit hardwood is bought and sold by. Enter the thickness and width in inches, the length in feet, and the number of boards, and it returns board feet per piece, the total, and the cost at your price per board foot.
Unlike construction lumber sold by the piece, hardwoods like oak, maple, walnut, and cherry are priced per board foot, and thickness is quoted in quarters (4/4, 8/4). Knowing how to calculate board feet before you visit the lumberyard lets you budget a project and check that an invoice matches what actually went in your truck.
How to Calculate Board Feet (Formula)
A board foot is the volume of a board 1 inch thick, 12 inches wide, and 1 foot long — 144 cubic inches. Two equivalent formulas:
- BF = (thickness in × width in × length ft) ÷ 12
- BF = (thickness in × width in × length in) ÷ 144
So a 1" × 6" × 8 ft board is (1 × 6 × 8) ÷ 12 = 4 board feet, and ten of them total 40 BF. Three important conventions: use nominal rough-sawn thickness (a surfaced 4/4 board still counts as 1 inch), round thickness under 1 inch up to 1 inch, and measure width at the board’s average point on waney or tapered stock.
The Quarter System: What 4/4, 5/4, and 8/4 Mean
Hardwood thickness is named in quarters of an inch, measured on the rough-sawn board before surfacing:
- 4/4 ("four quarter") = 1 in rough, about 13/16 in after surfacing
- 5/4 = 1.25 in rough, about 1-1/16 in surfaced — common for stair treads and decking
- 6/4 = 1.5 in rough, about 1-5/16 in surfaced
- 8/4 = 2 in rough, about 1-3/4 in surfaced — table legs and workbench tops
- 12/4 = 3 in rough — turning blanks and heavy legs
You pay board footage on the rough thickness, which is why an "inch-thick" surfaced board is billed as 4/4. Thicker stock also costs more per board foot because wide, thick boards are harder to dry without defects.
Worked Example: Pricing Lumber for a Bookshelf
Suppose a bookshelf design needs ten 4/4 red oak boards, each 6 inches wide and 8 feet long, and your hardwood dealer charges $4.00 per board foot.
Step 1 — board feet per piece: (1 × 6 × 8) ÷ 12 = 4 BF. Step 2 — total board feet: 4 × 10 = 40 BF. Step 3 — total cost: 40 × $4.00 = $160.
Smart buyers add 15–30% extra footage for defects, grain matching, and mistakes, so you would actually order about 48 BF ($192). If you upgraded the same design to 8/4 stock for the sides, each 2" × 6" × 8 ft board would be 8 BF — double the footage and, at 8/4 prices, more than double the cost.
Frequently Asked Questions
How do you calculate board feet?
Multiply thickness (inches) × width (inches) × length (feet) and divide by 12. A 1" × 6" × 8 ft board is (1 × 6 × 8) ÷ 12 = 4 board feet. If the length is in inches, divide by 144 instead of 12.
What is a board foot of lumber?
A board foot is a volume unit equal to a board 1 inch thick, 12 inches wide, and 12 inches long — 144 cubic inches. Hardwood lumber is priced per board foot because boards come in random widths and lengths, unlike dimensional construction lumber sold by the piece.
How many board feet are in a 2x4x8?
A 2×4 that is 8 feet long contains (2 × 4 × 8) ÷ 12 = 5.33 board feet using nominal dimensions. Note that construction lumber like 2×4s is normally sold by the piece, not by the board foot — board-foot pricing is standard for hardwoods.
What does 4/4 mean in lumber?
4/4 ("four quarter") means the board was sawn 1 inch thick — thickness is quoted in quarters of an inch. So 5/4 is 1.25 in, 6/4 is 1.5 in, and 8/4 is 2 in. After drying and surfacing, 4/4 stock finishes around 13/16 in, but you are billed on the full rough thickness.
How much does a board foot of lumber cost?
Domestic hardwoods typically run $3–$10 per board foot: red oak around $3–$5, hard maple $4–$7, walnut $8–$14, and cherry $5–$9. Exotics like teak can exceed $20–$40 per board foot. Prices rise with thickness, width, and grade, and vary by region.