Quick Answer

Ten 2x4 boards at 8 feet long have actual dimensions of 1.5" x 3.5" and total 53.33 board feet (5.33 BF per piece).

Nominal Size 2x4 2x6 2x8 2x10 2x12 4x4

Board Length (feet)

Quantity

Common Examples

Input	Result
2x4, 8 ft, 10 pieces	1.5" x 3.5" actual, 5.33 BF each, 53.33 BF total, 80 LF
2x6, 12 ft, 20 pieces	1.5" x 5.5" actual, 12.00 BF each, 240.00 BF total, 240 LF
2x10, 16 ft, 5 pieces	1.5" x 9.25" actual, 26.67 BF each, 133.33 BF total, 80 LF
2x12, 10 ft, 8 pieces	1.5" x 11.25" actual, 20.00 BF each, 160.00 BF total, 80 LF
4x4, 8 ft, 6 pieces	3.5" x 3.5" actual, 10.67 BF each, 64.00 BF total, 48 LF

How It Works

The Formula

Board Feet = (Nominal Thickness x Nominal Width x Length in feet) / 12

This formula uses nominal (named) dimensions, which is the standard practice in the lumber industry. Board feet represent a volume of wood, and pricing for many lumber products is based on this unit.

Nominal vs. Actual Dimensions

After sawing, drying, and planing, lumber shrinks from its rough-cut nominal size. The table below shows the standard conversions:

Nominal Size	Actual Size
2x4	1.5” x 3.5”
2x6	1.5” x 5.5”
2x8	1.5” x 7.25”
2x10	1.5” x 9.25”
2x12	1.5” x 11.25”
4x4	3.5” x 3.5”

These actual dimensions are standardized by the American Lumber Standard Committee and apply to kiln-dried, surfaced (S4S) lumber sold at lumber yards and home centers.

Why Nominal Sizes Differ

When a tree is first sawn, the boards are cut to the nominal dimensions (a 2x4 is truly 2 inches by 4 inches at the sawmill). Kiln drying reduces the moisture content and shrinks the wood slightly. Planing (surfacing) the boards smooth removes an additional fraction of an inch from each face. The result is a board that is 1/4 to 3/4 inch smaller in each dimension than the nominal name implies.

Board Feet vs. Linear Feet

Board feet measure volume; linear feet measure only length. A single 2x4 that is 8 feet long is 8 linear feet but only 5.33 board feet. The distinction matters for pricing: hardwood lumber is typically priced per board foot, while dimensional softwood lumber (the kind used for framing) is more often priced per linear foot or per piece.

Common Lumber Lengths

Standard dimensional lumber is sold in 2-foot increments: 8, 10, 12, 14, 16, 18, and 20 feet. Availability of longer lengths varies by region and lumber type.

Worked Example

For 10 pieces of 2x6 lumber at 12 feet each: Board feet per piece = (2 x 6 x 12) / 12 = 144 / 12 = 12.00 BF. Total board feet = 12.00 x 10 = 120.00 BF. Total linear feet = 12 x 10 = 120 LF. Actual dimensions are 1.5” x 5.5” per board. If the lumber is priced at $0.85 per linear foot, the total cost would be 120 x $0.85 = $102.00. If priced at $7.00 per board foot, the cost would be 120 x $7.00 = $840.00 (board foot pricing is more common for hardwoods and specialty wood).

Related Calculators

Board Feet Calculator

Calculate board feet for lumber based on thickness, width, length, and quantity.

Deck Calculator

Calculate decking boards, joists, posts, and beams needed for a deck based on dimensions and board specifications.

Frequently Asked Questions

Why is a 2x4 not actually 2 inches by 4 inches?

Dimensional lumber is named after its rough-cut size at the sawmill. After kiln drying and surface planing, the board shrinks to 1.5 inches by 3.5 inches. This convention has been standard in the lumber industry for decades and is regulated by the American Lumber Standard Committee.

What is the difference between board feet and linear feet?

Board feet is a unit of volume equal to a 1-inch thick, 12-inch wide, 1-foot long piece of wood (144 cubic inches). Linear feet measures only length, regardless of width or thickness. A 2x4 at 8 feet is 8 linear feet but 5.33 board feet. Hardwood is typically priced per board foot; softwood framing lumber is usually priced per piece or per linear foot.

When would I use 4x4 lumber?

4x4 lumber (actual 3.5" x 3.5") is primarily used for fence posts, deck railing posts, structural support posts, and pergola or arbor construction. It provides a square cross-section with sufficient strength for vertical load-bearing applications. For longer spans or heavier loads, 6x6 posts may be required.

How do I calculate lumber for a project with different sizes?

Calculate the board feet for each lumber size separately, then add the totals. For example, a project needing 20 pieces of 2x6 at 10 feet and 10 pieces of 2x4 at 8 feet: 2x6 BF = (2 x 6 x 10 / 12) x 20 = 200 BF. 2x4 BF = (2 x 4 x 8 / 12) x 10 = 53.33 BF. Total = 253.33 BF.

Does treated lumber have the same dimensions as untreated?

Yes, pressure-treated lumber has the same actual dimensions as untreated lumber of the same nominal size. A treated 2x4 is still 1.5" x 3.5". The treatment process forces preservative chemicals into the wood under pressure but does not change the board dimensions.