Lumber Board Feet Calculator
Understanding Board Feet Calculations
A Board Foot (BF) is a specialized unit of volume used in the United States and Canada for measuring lumber. It represents the volume of a piece of wood that is 12 inches long, 12 inches wide, and 1 inch thick. One board foot is equivalent to 144 cubic inches.
The Board Foot Formula
Depending on whether you are measuring length in feet or inches, use one of the following formulas:
- When length is in Feet: (Thickness" × Width" × Length') / 12
- When length is in Inches: (Thickness" × Width" × Length") / 144
Nominal vs. Actual Dimensions
When using this calculator, it is crucial to understand the difference between nominal size (the name used at the store, like a 2x4) and actual size (the physical measurement after surfacing). For hardwoods, lumber is often sold by its rough thickness in quarters:
- 4/4 (Four-Quarter): 1 inch thick rough, approx 3/4" - 13/16" surfaced.
- 5/4 (Five-Quarter): 1-1/4 inch thick rough, approx 1-1/16" surfaced.
- 8/4 (Eight-Quarter): 2 inches thick rough, approx 1-3/4" surfaced.
Lumber yards usually bill based on the nominal (rough) thickness, so if you are buying 4/4 lumber, you should input "1" into the thickness field even if the board has been planed down to 3/4".
Calculation Example
If you have 5 boards of Walnut that are 1 inch thick, 6 inches wide, and 8 feet long:
- Apply formula: (1" × 6" × 8') / 12 = 4 BF per board.
- Multiply by quantity: 4 BF × 5 boards = 20 Total Board Feet.
- If the price is $10.00 per board foot, your total cost is 20 × $10 = $200.00.
Tips for Buying Lumber
When estimating for a project, it is standard practice to add a waste factor of 15% to 20% to your total board feet. This accounts for knots, cracks (checking) at the ends of the boards, and grain matching requirements.