Lumber Calculator — Board Feet & Dimension Guide
Calculate board footage for hardwood ordering and framing estimates. Reference nominal versus actual dimensions for softwood lumber.
A Board Foot (BF) is a unit of volume equal to a board 12" wide, 12" long, and 1" thick (144 cubic inches). Formula: (Thickness" × Width" × Length') / 12. Note that hardwood is often sold by "quarters" (e.g., 4/4 is 1" thick).
Nominal vs. Actual Lumber Dimensions
| Nominal Size | Actual Size (Dry) | Actual Size (Green) |
|---|---|---|
| 1 × 4 | 3/4 × 3 1/2 | 25/32 × 3 9/16 |
| 2 × 4 | 1 1/2 × 3 1/2 | 1 9/16 × 3 9/16 |
| 2 × 6 | 1 1/2 × 5 1/2 | 1 9/16 × 5 5/8 |
| 2 × 10 | 1 1/2 × 9 1/4 | 1 9/16 × 9 1/2 |
| 4 × 4 | 3 1/2 × 3 1/2 | 3 9/16 × 3 9/16 |
Understanding Board Feet and Nominal Lumber Dimensions
In the carpentry and timber trades, purchasing lumber is rarely as simple as measuring its length. Wood is a three-dimensional product. While finish carpenters might purchase baseboard by the "linear foot," rough framing lumber and raw hardwoods are priced and sold by volume using a measurement called the "Board Foot."
What is a Board Foot?
A Board Foot (often abbreviated as BD FT or BF) is a specialized unit of volume used exclusively for timber. One board foot is defined as a piece of wood that is 12 inches wide, 12 inches long, and 1 inch thick (144 cubic inches). The formula to calculate board feet is: (Thickness in inches × Width in inches × Length in feet) ÷ 12. If you are buying a truckload of lumber, the mill will quote you a price per MBF (Thousand Board Feet).
Nominal vs. Actual Dimensions
The most confusing aspect of modern lumber calculation is the difference between nominal and actual dimensions. A "2x4" does not actually measure 2 inches by 4 inches. The term "2x4" is its nominal size—the size of the rough, green board when it was first cut at the sawmill. After the wood is kiln-dried (to prevent warping) and planed smooth (surfaced on all four sides, or S4S), its actual dimensions shrink to 1.5 inches by 3.5 inches.
Applying Board Feet to Rough Dimensions
Crucially, when calculating Board Feet for purchasing purposes, you must always use the nominal dimensions, not the actual planed dimensions. For example, a 10-foot long 2x4 is calculated as (2 × 4 × 10) ÷ 12, resulting in 6.66 Board Feet, even though its physical volume is significantly less.