What Is a Board Foot?

A board foot (abbreviated BF, bd ft, or FBM) is the standard unit for measuring lumber volume in the United States and Canada. It equals the volume of a piece of wood that is:

• 1 inch thick
• 12 inches (1 foot) wide
• 12 inches (1 foot) long

That's 144 cubic inches, or 1/12 of a cubic foot. Any combination of thickness, width, and length that multiplies to 144 cubic inches equals exactly one board foot — which is why the unit is so versatile for lumber in different shapes.

The Board Foot Formula

Example: a 2×4 board that is 8 feet long contains (2 × 4 × 8) ÷ 12 = 5.33 board feet (using nominal dimensions).

→ Full guide: How to calculate board feet with worked examples

Why Board Feet?

Lumber comes in many combinations of thickness, width, and length. A single unit that captures all three dimensions makes pricing, tallying, and comparing quantities straightforward. A sawyer selling 1" × 6" × 12' boards and 2" × 4" × 8' boards can price both at the same rate per board foot because one board foot represents the same volume of wood regardless of shape.

This is especially valuable when comparing rough-sawn boards of irregular widths, where a consistent volume-based unit eliminates guesswork. Sawmills, lumber dealers, and large contractors all quote prices in board feet (or MBF for large orders) for exactly this reason.

Board Foot Abbreviations Explained

The board foot has accumulated several abbreviations over its history in the North American lumber trade:

All of these abbreviations refer to the same underlying unit. The abbreviation varies by industry segment and era — you'll see FBM in older forestry documents and BF on modern invoices, but the math is identical.

Nominal vs Actual Dimensions

A common source of confusion: lumber is sold by nominal dimensions (the trade name, e.g., "2×4"), but the actual milled size is smaller. A "2×4" actually measures 1.5 inches × 3.5 inches after surfacing. Board foot calculations use whichever dimension you enter — the calculator does not automatically adjust for this.

This means a nominal 2×4×8 = 5.33 BF, while the same board measured at actual dimensions = 2.92 BF. Which one you use depends on context: use nominal when ordering from a lumber yard (to match how they sell it), and actual when calculating true material weight, volume for shipping, or engineering loads.

→ Nominal vs actual lumber dimensions — full reference guide

Hardwood vs Softwood: Quarter Sizing

Softwood framing lumber (2×4, 2×6, etc.) is sold in nominal whole-inch or half-inch thicknesses. Hardwood works differently: it is traditionally sold in quarter-inch increments, expressed as fractions with 4 in the denominator. This system comes from the historical practice of measuring rough-sawn boards at the sawmill before drying.

Hardwood tallying follows NHLA (National Hardwood Lumber Association) rules: thickness rounds up to the next quarter-inch; length rounds down to the nearest whole foot. Any board thinner than 4/4 is tallied as 4/4 — a minimum thickness floor. This is the industry standard for hardwood, implemented in the calculator's "Hardwood tally" mode.

The reason the rounding rules are asymmetric (up for thickness, down for length) is deliberate: it protects the buyer against getting less wood than paid for while acknowledging that sawn boards are never perfectly uniform.

Board Foot vs Cubic Foot

These two units measure the same thing — volume — but at different scales:

• 1 cubic foot = 12 board feet
• 1 board foot = 144 cubic inches = 1/12 cubic foot

The conversion is straightforward: divide board feet by 12 to get cubic feet. For example, 240 BF ÷ 12 = 20 cubic feet. This matters when calculating shipping weight, drying kiln capacity, or comparing to metric volumes. For the full set of volume conversions (including cubic meters and MBF), see the lumber volume conversions page.

MBF: Thousand Board Feet

For large commercial quantities, lumber is priced and measured in MBF (thousand board feet). 1 MBF = 1,000 board feet. If a sawmill quotes "$800/MBF," that's $0.80 per board foot. Wholesale hardwood is almost always priced in MBF; retail lumber yards typically use per-piece or per-BF pricing.

→ What is MBF? Full explanation with cost conversion tables

How Many Board Feet in Common Sizes?

All values use nominal dimensions. → See the full interactive board foot chart for every size and length combination.

Calculate Board Feet

Use the free calculator to compute board feet for any size board, with support for multiple boards, hardwood tally mode, pricing per BF or MBF, and waste allowance:

→ Open the Board Foot Calculator

Frequently Asked Questions