Why is a "2×4" not actually 2″ × 4″?

The "2×4" is the rough-cut nominal size before the board is planed and dried. The actual surfaced-dry size (PS 20 standard) is 1.5″ × 3.5″. Always use the actual size when fitting joinery.

How do I calculate board feet?

Board feet = (nominal thickness in inches × nominal width in inches × length in feet) ÷ 12. So a 2×6 × 10 ft = (2 × 6 × 10) ÷ 12 = 10 BF.

What is the difference between board feet and linear feet?

Linear feet is just the length. Board feet accounts for cross-section. Twenty pieces of 2×4 × 8 ft is 160 linear feet but 106.7 board feet.

What lumber lengths are commonly available?

Standard stock is 8, 10, 12, 14, 16, 18, and 20 feet, but 16-foot is the most common for joists and rafters. Specialty lengths up to 24 feet exist but at a premium.

Does this work for hardwood lumber?

For board-foot pricing yes — the formula is the same. But hardwood actual dimensions vary by mill (rough sawn vs. S2S vs. S4S), so verify the actual size when ordering.

Is the calculator free?

Yes — free, no signup, runs in your browser.

Lumber Calculator

Board feet, linear feet, and actual dimensions from nominal lumber size and length.

Written by Golam Rabbani, Founder & Lead Engineer

This interactive tool requires JavaScript. Read the formula and worked example below; you can compute the result by hand.

How to use this lumber calculator

Toggle between imperial (ft / in) and metric (m / mm).
Pick the nominal lumber size from the dropdown — for example 2×4, 2×6, or 4×4.
Enter the length per piece and the number of pieces.
Press Calculate to see board feet, linear feet, actual dimensions, and total volume.
Use Copy to save the result or Reset to start over.

About this lumber calculator

The lumber calculator converts a quantity of dimensional lumber into board feet, linear feet, and the surfaced-dry actual dimensions you will actually receive. North American softwood lumber is sold by its nominal (rough-cut) size, but a board planed and dried to PS 20 standard is smaller. A '2×4' has an actual dimension of 1.5 × 3.5 inches, a '2×6' is 1.5 × 5.5 inches, and a '4×4' is 3.5 × 3.5 inches. The calculator uses the published PS 20 table so you can size joinery and cuts correctly.

Board feet (BF) is the standard unit for hardwood and large-volume softwood purchases. The formula is BF = (nominal-T inches × nominal-W inches × length in feet) ÷ 12. A 2×4 at 8 feet = (2 × 4 × 8) ÷ 12 = 5.33 BF. Twenty of those is 106.7 BF, which is roughly what a deck or wall framing pack would be priced on.

Worked example: 20 pieces of 2×6 at 12 feet. Board feet = (2 × 6 × 12) ÷ 12 × 20 = 240 BF. Linear feet = 20 × 12 = 240 ft = 73.15 m. Actual dimensions are 1.5″ × 5.5″ (38.1 × 139.7 mm). Total cubic volume is 0.32 m³. That is enough lumber for a standard deck frame of 12 × 16 feet, joists at 16″ on-centre.

FAQ

Why is a "2×4" not actually 2″ × 4″?: The "2×4" is the rough-cut nominal size before the board is planed and dried. The actual surfaced-dry size (PS 20 standard) is 1.5″ × 3.5″. Always use the actual size when fitting joinery.
How do I calculate board feet?: Board feet = (nominal thickness in inches × nominal width in inches × length in feet) ÷ 12. So a 2×6 × 10 ft = (2 × 6 × 10) ÷ 12 = 10 BF.
What is the difference between board feet and linear feet?: Linear feet is just the length. Board feet accounts for cross-section. Twenty pieces of 2×4 × 8 ft is 160 linear feet but 106.7 board feet.
What lumber lengths are commonly available?: Standard stock is 8, 10, 12, 14, 16, 18, and 20 feet, but 16-foot is the most common for joists and rafters. Specialty lengths up to 24 feet exist but at a premium.
Does this work for hardwood lumber?: For board-foot pricing yes — the formula is the same. But hardwood actual dimensions vary by mill (rough sawn vs. S2S vs. S4S), so verify the actual size when ordering.
Is the calculator free?: Yes — free, no signup, runs in your browser.