Board Foot Calculator - Lumber Volume Calculator
Calculate board feet from lumber thickness, width, and length in inches. Free calculator with the board foot formula, a worked example, and a size chart.
Board Foot Calculator
Calculates the volume of lumber in board feet from thickness, width, and length in inches.
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Formula
Board Feet = (Thickness × Width × Length) ÷ 144
(1 × 4 × 8) ÷ 144 = 0.22
Visualization
Documentation
What is a board foot?
A board foot is a unit for measuring the volume of lumber. One board foot equals a piece of wood 12 inches long, 12 inches wide, and 1 inch thick, or 144 cubic inches. Lumber yards in the United States and Canada price and sell most hardwood, and much softwood, by the board foot rather than by length alone. This lets buyers compare a thick, narrow board against a thin, wide one on equal terms, the same way shoppers compare food by weight instead of by package size.
Board foot formula
The formula is:
Board feet = (thickness × width × length) ÷ 144
All three dimensions go in inches. The result is 144 because that is how many cubic inches make up one board foot (12 × 12 × 1). Dividing the total cubic inches of a board by 144 converts that volume into board feet.
If any dimension is zero or negative, the board has no usable volume, so the result is 0.
How to calculate board feet
- Measure thickness, width, and length in inches. If length was measured in feet, multiply by 12 first (an 8-foot board is 96 inches).
- Multiply thickness × width × length.
- Divide the result by 144.
Lumber is often sold by its nominal size, such as "2×4" or "1×6," but the board's actual size after drying and planing is smaller. A nominal 2×4 actually measures 1.5 by 3.5 inches when dry. Lumber yards price by the nominal size. Builders and woodworkers should use the actual size when planning cuts, since that is what they can physically work with.
Example
A board measures 2 inches thick, 6 inches wide, and 8 feet (96 inches) long.
Board feet = (2 × 6 × 96) ÷ 144 = 1,152 ÷ 144 = 8 board feet
For a project needing ten of these boards, the total is 80 board feet (10 × 8). At 480. Woodworkers usually order some extra to cover cutting waste and defects.
Common lumber sizes and their board feet
Board feet for standard nominal sizes, each 8 feet long:
| Nominal size | Board feet (8 ft length) |
|---|---|
| 1 × 4 | 2.67 |
| 1 × 6 | 4.00 |
| 1 × 8 | 5.33 |
| 1 × 12 | 8.00 |
| 2 × 4 | 5.33 |
| 2 × 6 | 8.00 |
| 2 × 8 | 10.67 |
| 2 × 10 | 13.33 |
| 2 × 12 | 16.00 |
| 4 × 4 | 10.67 |
| 6 × 6 | 24.00 |
These figures use nominal dimensions, which is how lumber is priced. Actual (measured) dimensions are smaller and would give lower board-foot totals.
Nominal vs. actual dimensions
| Nominal size | Actual size (inches) |
|---|---|
| 1 × 4 | 0.75 × 3.5 |
| 1 × 6 | 0.75 × 5.5 |
| 1 × 8 | 0.75 × 7.25 |
| 1 × 12 | 0.75 × 11.25 |
| 2 × 4 | 1.5 × 3.5 |
| 2 × 6 | 1.5 × 5.5 |
| 2 × 8 | 1.5 × 7.25 |
| 2 × 12 | 1.5 × 11.25 |
These are the minimum dry dressed sizes for American Standard lumber. The gap between nominal and actual size comes from drying and surface planing at the mill. Rough lumber shrinks as it dries, and planing removes a further thin layer to make each face smooth and flat.
Board feet compared with other measurements
- Cubic feet: 1 cubic foot equals 12 board feet.
- Cubic meters: 1 cubic meter equals roughly 424 board feet.
- Linear feet: measures only length, ignoring width and thickness. Used for trim and molding sold by length.
- Square feet: measures surface area only, ignoring thickness. Used for flooring and sheet materials.
- Plywood and sheet goods: sold by the sheet or by square foot, not by board foot. A standard 4×8-foot sheet covers 32 square feet.
Tips for accurate calculations
- Measure a board in more than one spot; width and thickness can vary along its length.
- Convert everything to inches before multiplying. Mixing feet and inches is the most common source of error.
- For a board with an irregular or wavy edge, split it into straight sections, calculate each one, and add the results.
- Add extra for waste, and more for rough lumber that still needs planing.
- Board foot calculations do not apply to standing logs. Logs are measured with separate log rules, such as the Doyle, Scribner and International rules, that estimate the lumber a log will yield after milling.
Frequently asked questions
What is a board foot? A unit of lumber volume equal to 144 cubic inches, the same as a piece 12 inches long, 12 inches wide, and 1 inch thick.
How do I calculate board feet? Multiply thickness, width, and length, all in inches, then divide by 144. A 2×6 board 96 inches long gives (2 × 6 × 96) ÷ 144 = 8 board feet.
Why does the formula divide by 144? Because 144 cubic inches make up one board foot (12 inches × 12 inches × 1 inch). Dividing a board's total cubic inches by 144 converts it to board feet.
Should I use nominal or actual dimensions? Use nominal dimensions (like 2×4) for pricing, since that is how lumber yards sell it. Use actual dimensions (like 1.5 × 3.5 inches) when planning cuts and joinery.
How do board feet relate to cubic feet? One cubic foot equals 12 board feet. Divide a board-foot total by 12 to get cubic feet.
Does this formula work for plywood or logs? No. Plywood and sheet goods are sold by the sheet or by square foot. Logs use separate scaling rules that account for bark, taper, and defects.
References
- Purdue University Cooperative Extension Service. Log and Tree Scaling Techniques (FNR-191). Purdue FNR-191 — Doyle, Scribner and International are the widely used log rules.
- USDA Forest Products Laboratory. Wood Handbook (FPL-GTR-282), Chapter 6: Commercial Lumber, Round Timbers, and Ties. Wood Handbook, chapter 6 — Table 6–6 nominal and minimum dressed dry sizes (nominal 1 → 3/4 in, 2 → 1-1/2 in; widths 4 → 3-1/2, 6 → 5-1/2, 8 → 7-1/4, 12 → 11-1/4 in).