Step 1
Measure the actual board size
Start with the actual thickness, width, and length of the board. Hardwood dealers and sawmills may list lumber by rough thickness such as 4/4, 5/4, or 8/4. Surfaced boards and construction lumber often finish smaller than nominal size, so always measure the real board when you need an accurate quote.
For example, a full rough 8/4 board is roughly 2 inches thick. A surfaced 2 x 4 is not actually 2 inches by 4 inches. That difference changes the final board foot number.
Step 2
Apply the standard board foot formula
When all dimensions are in inches, use this equation:
Board Feet = (Thickness x Width x Length x Pieces) / 144
If length is already in feet, the quick version is:
Board Feet = (Thickness x Width x Length in feet x Pieces) / 12
Both formulas return the same answer. The only difference is whether you convert the board length into inches first.
Step 3
Work through a real example
Suppose you have 8 boards that each measure 2 inches thick, 6 inches wide, and 8 feet long.
- Thickness = 2 inches
- Width = 6 inches
- Length = 8 feet
- Pieces = 8
Use the shortcut formula: (2 x 6 x 8 x 8) / 12 = 64 board feet.
If your supplier charges $3.25 per board foot, the estimated cost is 64 x 3.25 = $208.00.
Mistakes
Common board foot mistakes
- Using square footage without thickness. Board feet is a volume measure, so thickness is required.
- Mixing inches and feet inside the same formula without converting correctly.
- Using nominal dimensions when the supplier prices on actual surfaced measurements.
- Forgetting to multiply by the number of boards in the order.
Fastest Method
Use the calculator for repeat estimates
When you are comparing multiple board sizes, the calculator is faster and reduces mistakes. You can also pin known values, such as width or price per board foot, and let the tool solve for the remaining number.