What Is a Board Foot?
A board foot is the standard unit for measuring and pricing hardwood lumber in the United States. One board foot equals a piece of wood one inch thick, twelve inches wide, and twelve inches long — or 144 cubic inches of wood in any configuration. Whether you're pricing rough-sawn walnut for a dining table or ordering framing lumber for a deck, board feet are how lumber is sold.
The formula is straightforward:
When length is measured in feet instead of inches (which is more common at the lumberyard), the formula simplifies:
Both formulas produce the same result. This calculator accepts length in either feet or inches — use the toggle next to the length field.
Nominal vs. Actual Lumber Dimensions
This is where most DIYers get tripped up. When you buy a "2×4" at the hardware store, the board is not two inches by four inches. It's 1.5 inches by 3.5 inches. The nominal size (2×4) refers to the rough-sawn dimensions before the board is dried and planed smooth. The actual size is what you hold in your hand.
This matters for board foot calculations. If you're buying softwood from a home centre and enter "2" and "4" into a board foot calculator, you'll overestimate by about 25%. This calculator's preset dropdown uses actual dimensions so your numbers are accurate from the start.
Common Nominal vs. Actual Sizes
| Nominal Size | Actual Size (inches) | BF per Linear Foot |
|---|---|---|
| 1×4 | 0.75 × 3.5 | 0.22 |
| 1×6 | 0.75 × 5.5 | 0.34 |
| 1×8 | 0.75 × 7.25 | 0.45 |
| 1×10 | 0.75 × 9.25 | 0.58 |
| 1×12 | 0.75 × 11.25 | 0.70 |
| 2×4 | 1.5 × 3.5 | 0.44 |
| 2×6 | 1.5 × 5.5 | 0.69 |
| 2×8 | 1.5 × 7.25 | 0.91 |
| 2×10 | 1.5 × 9.25 | 1.16 |
| 2×12 | 1.5 × 11.25 | 1.41 |
| 4×4 | 3.5 × 3.5 | 1.02 |
| 6×6 | 5.5 × 5.5 | 2.52 |
Note: these actual dimensions apply to kiln-dried softwood lumber (pine, spruce, fir) sold at home centres. Rough-sawn hardwood is typically sold at full nominal dimensions — a 4/4 (one-inch) hardwood board is actually one inch thick before surfacing.
How Hardwood Lumber Is Sold
Hardwood lumber uses a different sizing system called the "quarter system." Thickness is expressed in quarters of an inch:
| Quarter Designation | Rough Thickness | Surfaced (S2S) |
|---|---|---|
| 4/4 ("four-quarter") | 1″ | 13/16″ |
| 5/4 ("five-quarter") | 1.25″ | 1-1/16″ |
| 6/4 ("six-quarter") | 1.5″ | 1-5/16″ |
| 8/4 ("eight-quarter") | 2″ | 1-13/16″ |
| 12/4 ("twelve-quarter") | 3″ | 2-13/16″ |
Hardwood is priced per board foot, and the price varies enormously by species. Poplar might run $3 to $5 per board foot. Cherry and maple sit in the $6 to $10 range. Walnut can reach $12 to $18 or more for select grades. Exotic species like purpleheart or zebrawood can exceed $25 per board foot.
Board Feet for Common Projects
To give you a rough sense of scale, here are typical board foot requirements for common woodworking and construction projects:
| Project | Approx. Board Feet |
|---|---|
| Cutting board | 2–4 BF |
| Small bookshelf | 15–25 BF |
| Dining table (6-seat) | 30–50 BF |
| Kitchen cabinets (full set) | 150–250 BF |
| 12×16 deck (framing + decking) | 300–500 BF |
| Built-in bookshelves (floor-to-ceiling) | 80–120 BF |
These are rough estimates. Actual quantities depend on your design, waste factor, and whether you're using solid wood or a combination of solid wood and plywood. For furniture projects, add 15 to 20% for waste from offcuts, defects, and milling loss.
Tips for Buying Lumber by the Board Foot
At a hardwood dealer, boards are sold in random widths and lengths. You don't get to pick exact sizes the way you do at a home centre. The dealer calculates board feet for each board and prices accordingly. A few things to keep in mind:
First, always buy more than your calculated total. Hardwood has natural defects — knots, sapwood, checks — and you'll lose material to jointing, planing, and crosscutting. A 20% overage is standard practice for furniture projects.
Second, wider boards cost more per board foot than narrow ones. A 10-inch-wide walnut board might be priced $2 to $4 per board foot higher than a 5-inch-wide board of the same species and grade. This is because wide boards come from larger, older trees and are less common.
Third, lumber is measured at its rough dimensions, even if you plan to surface it. Buying 4/4 rough lumber gives you about 13/16 of an inch of usable thickness after surfacing both faces. Plan your project dimensions around the finished thickness, not the rough stock.