Board Foot Calculator
Calculate board feet and estimate lumber cost from thickness, width, and length.
Common Lumber Sizes
| Nominal | Actual (in) | BF per 8 ft |
|---|---|---|
| 1×4 | 0.75 × 3.5 | 1.75 |
| 1×6 | 0.75 × 5.5 | 2.75 |
| 1×8 | 0.75 × 7.25 | 3.63 |
| 1×10 | 0.75 × 9.25 | 4.63 |
| 1×12 | 0.75 × 11.25 | 5.63 |
| 2×4 | 1.5 × 3.5 | 3.50 |
| 2×6 | 1.5 × 5.5 | 5.50 |
| 2×8 | 1.5 × 7.25 | 7.25 |
| 2×10 | 1.5 × 9.25 | 9.25 |
| 2×12 | 1.5 × 11.25 | 11.25 |
| 4/4 hardwood | 1.0 × varies | width ÷ 1.5 |
| 8/4 hardwood | 2.0 × varies | width × 1.33 |
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How to Calculate Board Feet
A board foot is a unit of volume equal to 144 cubic inches — equivalent to a piece of wood 1 inch thick, 12 inches wide, and 12 inches long. Lumber yards price hardwood by the board foot, making this calculation essential for project planning and budgeting.
The formula is straightforward: multiply thickness (inches) by width (inches) by length (inches), then divide by 144. For length in feet, the formula simplifies to: (thickness × width × length in feet) ÷ 12.
When buying rough-sawn hardwood, thickness is often expressed in quarters: 4/4 is 1 inch, 5/4 is 1.25 inches, 6/4 is 1.5 inches, and 8/4 is 2 inches. These are rough thicknesses before planing.
One board foot = 1 foot × 1 foot × 1 inch thick = 144 cubic inches. Formula: board feet = (thickness in inches × width in inches × length in feet) / 12. For a board 1.5 inches thick, 8 inches wide, and 8 feet long: (1.5 × 8 × 8) / 12 = 96/12 = 8 board feet.
Lumber is sold by the board foot for hardwoods; softwood dimensional lumber (2×4, 2×6 etc.) is typically sold by the linear foot or piece. Most hardwood dealers list price per board foot; multiply by total board feet calculated to get cost.
Yield and waste: rough lumber requires milling (jointing, planing, ripping) before use. A rough board sold as 4/4 (nominally 1 inch thick) mills down to about 13/16 inch — factor in this loss. Plan for 15–20% waste for straight grain stock and 25–30% for figured or short boards where you need to work around defects.
Common hardwood thicknesses: 4/4 (1"), 5/4 (1.25"), 6/4 (1.5"), 8/4 (2"), where the numerator is eighths of an inch. These are rough sawn dimensions — final dressed thickness after milling is typically 3/16 inch thinner. A 4/4 board dressed S2S finishes at roughly 13/16 inch.
See also: Miter Angle Calculator · Wood Shrinkage Calculator