What Is a Board Foot?
A board foot is the standard unit of measurement for hardwood lumber. Unlike buying 2x4s by the stick at a home center, purchasing rough lumber requires you to understand volume. Here is everything you need to know to calculate board feet accurately.
Board Foot Definition
In North America, a board foot (BF or bd ft) is a specialized unit of volume used for measuring lumber. It is defined as the volume of a one-foot length of a board that is one foot wide and one inch thick.
Mathematically, one board foot equals exactly 144 cubic inches of wood. Whether the wood is thin and wide, or thick and narrow, if the total volume reaches 144 cubic inches, it equals one board foot.
The Board Foot Formula
Calculating board feet is straightforward once you know your board's nominal dimensions. You can use either of the following formulas depending on how you measure the length:
*Where all measurements (T, W, L) are in inches.
*Where Thickness and Width are in inches, but Length is in feet.
Important: Calculations are based on nominal (rough) dimensions. If you are buying a surfaced 3/4-inch board, you are paying for the 4/4 (1-inch) rough stock it was milled from.
Worked Examples
Let's look at a few common scenarios you might encounter at the lumberyard:
- Example 1: A standard 1" × 6" board that is 8 feet long.
Calculation: (1" × 6" × 8ft) ÷ 12 = 4 board feet. - Example 2: A thick 2" × 8" plank that is 10 feet long.
Calculation: (2" × 8" × 10ft) ÷ 12 = 13.33 board feet. - Example 3: Rough-sawn 8/4 (2") walnut, 7" wide, 6 feet long.
Calculation: (2" × 7" × 6ft) ÷ 12 = 7 board feet.
Board Feet vs Linear Feet vs Square Feet
It is crucial not to mix up these three lumber measurements:
- Board Feet (Volume): Measures total volume (T × W × L). Used primarily for random-width rough hardwood lumber.
- Linear Feet (Length): Measures length only. Used for trim, molding, and standard dimensional lumber (like a 2x4) where thickness and width are already fixed.
- Square Feet (Area): Measures area (W × L). Used for sheet goods like plywood, MDF, or flooring where thickness is standardized.
Why Lumber Is Sold by the Board Foot
When a sawmill processes a hardwood log, cutting boards to uniform widths results in massive waste. Instead, the log is sliced to a consistent thickness (like 4/4 or 8/4), but the boards are left in random widths and random lengths.
Because every board is a different size, pricing them by the "piece" or "linear foot" is impossible. Board feet standardize the pricing so you are paying strictly for the total volume of wood material you purchase.
Frequently Asked Questions
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