Board Foot Calculator
Calculate exactly how many board feet are in your lumber. Enter your dimensions below to instantly find total wood volume, square footage equivalents, and estimate project costs.
Whether you are a professional woodworker buying raw hardwood from a local mill, or a DIYer planning a deck, understanding how lumber is priced and measured is a vital skill. While big box stores often sell construction lumber by the “piece” or “linear foot”, professional sawmills sell wood by its true volume: the Board Foot.
Our free Board Foot Calculator removes the confusing math from estimating lumber. By entering your wood’s dimensions and quantity, this tool instantly calculates the total board footage, linear length, and estimated project cost.
What is a Board Foot?
A board foot (often abbreviated as BF, bd ft, or FBM for “Foot Board Measure”) is a specialized unit of volume used primarily in the United States and Canada for measuring lumber. It is not a measurement of length or surface area, but rather how much raw material exists in the piece of wood.
Exactly one board foot is equal to the volume of a piece of wood that is 1 inch thick, 12 inches wide, and 1 foot (12 inches) long.
Therefore, a single board foot is equal to exactly 144 cubic inches of wood. A thick, narrow piece of wood can have the exact same board footage as a thin, wide piece, so long as their total volumes are identical.
How to Calculate Board Feet (The Formulas)
Calculating board feet requires knowing three dimensions: the thickness, the width, and the length. Because lumber lengths are usually talked about in feet, while thickness and width are measured in inches, the standard formula uses a combination of units.
If Length is in Feet:
BD FT = (Thickness" × Width" × Length') ÷ 12
If Length is in Inches:
BD FT = (Thickness" × Width" × Length") ÷ 144
Step-by-Step Example: How many board feet is a 2x4x8?
Let’s calculate the volume of a standard 2×4 stud that is 8 feet long.
- Multiply the dimensions: 2 inches (Thickness) × 4 inches (Width) × 8 feet (Length) = 64.
- Divide by 12: 64 ÷ 12 = 5.33 Board Feet.
Understanding Hardwood Lumber Sizing (4/4, 5/4, 8/4)
If you visit a specialty hardwood dealer, you won’t see tags that say “1 inch thick.” Instead, raw hardwood is milled and sold using the “quarter system.” This system indicates the rough-sawn thickness of the board in quarters of an inch.
- 4/4 (Four-Quarters): 1 inch thick. This is the baseline. A 4/4 board that is 12 inches wide and 1 foot long is exactly 1 Board Foot.
- 5/4 (Five-Quarters): 1.25 inches thick. Often used for decking or thicker tabletops.
- 6/4 (Six-Quarters): 1.5 inches thick.
- 8/4 (Eight-Quarters): 2 inches thick. An 8/4 board contains twice as many board feet as a 4/4 board of the same length and width.
- 12/4 (Twelve-Quarters): 3 inches thick. Used for heavy table legs or structural beams.
Calculations for board feet are historically based on the nominal size of the lumber before it is planed and surfaced. A standard “2×4″ actually measures 1.5″ x 3.5”, but you still calculate its board footage using the 2 and 4. When buying rough-sawn hardwood, you calculate based on its rough thickness (e.g., 4/4 = 1 inch), even though you will lose some of that thickness when you plane it smooth.
Board Feet vs. Linear Feet vs. Square Feet
It is easy to confuse these three distinct measurements when estimating materials for a project.
- Linear Feet (LF): A simple measurement of length. If you lay three 10-foot long boards end-to-end, you have 30 linear feet of wood, regardless of how wide or thick the boards are. Baseboards and molding are priced by the linear foot.
- Square Feet (Sq Ft): A measurement of 2D surface area (Length × Width). If you are covering a 10×10 room, you need 100 square feet of flooring. It ignores thickness entirely.
- Board Feet (BF): A 3D volumetric measurement (Length × Width × Thickness).
How to convert Square Feet to Board Feet: Simply multiply your required square footage by the thickness of your wood in inches. If you need 200 square feet of decking, and you are using 2-inch thick boards, you must purchase 400 Board Feet of lumber (200 sq ft × 2 inches = 400 BF).
Common Lumber Board Feet Chart
Use this quick reference chart to find the board footage for standard dimensional construction lumber.
| Nominal Size | 8 Foot Length | 10 Foot Length | 12 Foot Length | 16 Foot Length |
|---|---|---|---|---|
| 1×4 | 2.67 BF | 3.33 BF | 4.00 BF | 5.33 BF |
| 1×6 | 4.00 BF | 5.00 BF | 6.00 BF | 8.00 BF |
| 2×4 | 5.33 BF | 6.67 BF | 8.00 BF | 10.67 BF |
| 2×6 | 8.00 BF | 10.00 BF | 12.00 BF | 16.00 BF |
| 2×8 | 10.67 BF | 13.33 BF | 16.00 BF | 21.33 BF |
| 4×4 | 10.67 BF | 13.33 BF | 16.00 BF | 21.33 BF |
Board Foot Calculator Frequently Asked Questions
To calculate board feet, multiply the nominal thickness in inches by the width in inches by the length in feet, and then divide the total by 12. The formula is: (Thickness × Width × Length in ft) ÷ 12.
A standard 2×4 that is 8 feet long contains roughly 5.33 board feet. The exact math is (2 × 4 × 8) ÷ 12 = 5.333 bd ft.
A 1×12 board that is 12 feet long contains exactly 12 board feet. Because the thickness is exactly 1 inch, the board footage perfectly matches its linear footage and square footage: (1 × 12 × 12) ÷ 12 = 12 bd ft.
Twenty board feet represents a specific volumetric amount of wood. It is equivalent to the volume of a solid piece of wood that is 1 inch thick, 12 inches wide, and 20 feet long. It can be made up of a single large board or several dozen smaller boards bundled together.
If the wood you are buying is 1 inch thick (4/4 nominal), 20 board feet will cover exactly 20 square feet of flat surface area. However, if the wood is 2 inches thick, that same 20 board feet will only cover 10 square feet of surface.
A 2×6 board that is 10 feet long contains exactly 10 board feet. The calculation is (2 inches × 6 inches × 10 feet) ÷ 12 = 10 bd ft.
Reference: https://en.wikipedia.org/wiki/Board_foot