How to Calculate Board Feet (With Examples)

What Is a Board Foot?

A board foot is the standard unit of measurement for hardwood lumber and many specialty softwood products. One board foot equals a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long — or any equivalent volume. Think of it as 144 cubic inches of wood.

Why not just use linear feet? Because hardwood lumber comes in random widths and lengths. A stack of walnut boards might include pieces ranging from 4 inches to 12 inches wide and 6 feet to 14 feet long. Board feet gives you a fair way to price wood regardless of the specific dimensions of each piece.

The Formula

The calculation is straightforward:

Board Feet = (Thickness in inches × Width in inches × Length in inches) ÷ 144

Or, if you measure length in feet (which is more common):

Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12

Example 1: A Single Board

You have a board that is 1 inch thick, 8 inches wide, and 10 feet long.

Board Feet = (1 × 8 × 10) ÷ 12 = 80 ÷ 12 = 6.67 board feet

Example 2: Thicker Stock

A piece of 8/4 (two-inch-thick) cherry that's 6 inches wide and 8 feet long.

Board Feet = (2 × 6 × 8) ÷ 12 = 96 ÷ 12 = 8 board feet

Note the thickness notation: hardwood is sold in "quarter" increments. 4/4 means 1 inch thick (four quarters). 8/4 means 2 inches thick. 6/4 means 1.5 inches thick. This is the rough-sawn thickness before any planing.

Example 3: A Pile of Boards

You're buying five boards of 4/4 red oak, each 6 inches wide and 8 feet long.

Each board = (1 × 6 × 8) ÷ 12 = 4 board feet

Five boards = 4 × 5 = 20 board feet

Example 4: Converting a Project to Board Feet

You're building a tabletop that will be 36 inches wide, 72 inches long, and 1 inch thick (finished). You need to estimate how much rough lumber to buy.

Finished volume: (1 × 36 × 72) ÷ 144 = 18 board feet.

But you need to account for waste. Rough boards need to be planed (losing about 3/16 inch per face), jointed (losing width on each edge), and crosscut (losing length to defects and squaring). A standard rule of thumb is to add 20-30% for waste.

18 board feet × 1.25 = 22.5 board feet (with 25% waste factor)

Common Gotchas

• Nominal vs. actual: Board feet for hardwood use the nominal (rough-sawn) thickness. A 4/4 board that's been surfaced to 13/16 inch is still sold as 1 inch thick for board foot pricing.
• Minimums: Many lumber yards sell hardwood in full boards. If you only need 3 board feet of walnut, you'll likely need to buy the whole board and keep the remainder.
• Width rounding: Boards are typically measured to the nearest half inch for width calculations. A board that's 7-1/4 inches wide is usually tallied as 7 inches.

When Board Feet Don't Apply

Dimensional softwood lumber (2x4s, 2x6s, etc.) is sold by the linear foot or per piece, not by board feet. Plywood and sheet goods are sold by the sheet. Board feet apply primarily to hardwood lumber and specialty softwoods.

When you request a hardwood quote, include your project dimensions and the waste factor you've calculated, so partner suppliers can quote enough material without overselling.