How to Calculate Board Feet: A Complete Guide

Lumber is one of the few building materials sold using its own unique unit of measurement. While framing lumber is priced by the linear foot, hardwoods and specialty woods are sold by the board foot. Understanding board feet is essential for buying wood for furniture, cabinetry, or any project using rough-sawn lumber.

The Board Foot Formula

A board foot equals a piece of wood 1 inch thick, 12 inches wide, and 12 inches long — or 144 cubic inches. The formula is:

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

For example, a board that is 2 inches thick, 6 inches wide, and 8 feet long:

Board Feet = (2 x 6 x 8) / 12 = 8 board feet

If priced at $6.50 per board foot, the board costs $52.00.

What Is a Board Foot?

A board foot is a measure of volume, not a specific board size. It is the standard pricing unit at hardwood dealers across the United States because hardwoods are milled in random widths and lengths. Pricing by volume lets you compare costs regardless of specific board dimensions.

When thickness uses "quarter" notation, it refers to quarter-inches of rough stock. 4/4 lumber is 1 inch thick, 6/4 is 1.5 inches, and 8/4 is 2 inches. These measurements are the rough-sawn dimension before planing.

When You Need This Calculator

• Woodworkers planning a furniture build who need to estimate board feet of walnut, oak, or maple from a hardwood dealer.
• Contractors pricing custom trim or millwork who need accurate footage for cost estimates and bids. For roof sheathing estimates, pair this with the Roofing Calculator.
• Hobbyists buying from a sawmill who want to verify that price per board foot matches the actual volume received.

Common Lumber Sizes

Board feet per linear foot for common sizes:

• 1 x 6: 0.50 BF per linear foot
• 1 x 8: 0.67 BF per linear foot
• 1 x 12: 1.00 BF per linear foot
• 2 x 4: 0.67 BF per linear foot
• 2 x 6: 1.00 BF per linear foot
• 2 x 12: 2.00 BF per linear foot

Hardwood dealers typically price using nominal rough-sawn dimensions, not surfaced dimensions.

Common Mistakes to Avoid

• Confusing nominal and actual dimensions. A 2x4 actually measures 1.5 x 3.5 inches. For surfaced lumber, use actual dimensions. For rough-sawn hardwood, use the stated quarter thickness.
• Mixing up feet and inches in the formula. Length in inches uses a divisor of 144; length in feet uses 12. The wrong divisor gives a result off by a factor of 12.
• Forgetting waste. Rough lumber has defects and irregular edges. Plan for 15 to 25 percent waste when converting rough boards into finished pieces. For fencing projects, the Fence Calculator accounts for picket and rail waste separately.
• Ignoring grade differences. FAS grade hardwood costs more than No. 1 Common but yields more usable material per board foot.

Pro Tips

• Buy in bulk. Many dealers discount orders over 100 board feet. Buying ahead for upcoming projects can save 10 to 20 percent.
• Verify at the yard. Bring a tape measure and calculator. Reputable dealers are happy to let you check their math.
• Use rough thickness for calculations. A 4/4 board planed to 3/4 inch is still priced at 1 inch thick.
• Factor in milling losses. Planing removes about 1/8 inch per side. A 4/4 board finishes at roughly 3/4 inch. Plan your material list based on finished dimensions plus milling allowance.

Frequently Asked Questions

How many board feet are in a 2x4x8?

Using nominal dimensions (2 x 4 x 8 feet), a 2x4x8 contains 5.33 board feet. However, framing lumber is usually sold by the linear foot or per piece, not by board footage. Board foot pricing is primarily for hardwoods.

What is the difference between a board foot and a linear foot?

A linear foot measures only length, regardless of width or thickness. A board foot measures volume. A 1x12 one foot long equals 1 board foot; a 1x6 one foot long equals 0.5 board feet. Linear foot pricing is for framing lumber; board foot pricing is for hardwoods.

Why is hardwood sold by the board foot?

Hardwood logs vary widely in diameter, so boards come in random widths and lengths. Pricing by volume creates a fair system regardless of dimensions, unlike softwood framing lumber which is manufactured to standard sizes.