Board Foot Formula: How to Calculate Lumber Volume
Last Updated: 2025-12-27
Learn the board foot formula: BF = (Thickness × Width × Length) ÷ 144. See examples, common sizes, and tips for accurate lumber calculations.
1 board foot = 1" × 12" × 12" = 144 cubic inches
BF = (T × W × L) ÷ 144
T, W, L are measurements. Use inches for the ÷144 version.
What is a board foot?
A board foot (BF) is a unit of lumber volume. It helps you compare wood by how much material you are buying, not just by length.
The key number is 144, because 144 = 12 × 12. It converts cubic inches into board feet.
The formula (3 versions)
All inches (standard)
BF = (T(in) × W(in) × L(in)) ÷ 144Use this when thickness, width, and length are all in inches.
Length in feet
BF = (T(in) × W(in) × L(ft)) ÷ 12Use this when your length is in feet.
Quick memory version
BF = (T(in) × W(in)) ÷ 12 × L(ft)Same math as the feet version, just grouped to remember faster.
How to calculate board feet (steps)
- Measure thickness:Measure the thickness of the board in inches (T).
- Measure width:Measure the width of the board in inches (W).
- Measure length:Measure the length of the board in feet (L).
- Apply the formula:Multiply T × W × L, then divide by 12 to get board feet.
Examples (with a common warning)
Nominal vs actual size
Use actual size, not nominal. A 2×4 is usually 1.5" × 3.5".
Example 1: 1" × 6" × 8' = 4 BF
BF = (1 × 6 × 8) ÷ 12 = 4
Example 2: 2×4×8 (actual 1.5" × 3.5") = 3.5 BF
BF = (1.5 × 3.5 × 8) ÷ 12 = 3.5
Example 3: 1" × 12" × 1' = 1 BF
BF = (1 × 12 × 1) ÷ 12 = 1
Common sizes (nominal vs actual)
| Nominal Size | Actual Size (in) | BF per Linear Foot | Notes |
|---|---|---|---|
| 1×4 | 0.75" × 3.5" | 0.22 | Common softwood size |
| 1×6 | 0.75" × 5.5" | 0.34 | Common softwood size |
| 1×8 | 0.75" × 7.25" | 0.45 | Common softwood size |
| 1×12 | 0.75" × 11.25" | 0.70 | Common softwood size |
| 2×4 | 1.5" × 3.5" | 0.44 | Most common framing size |
| 2×6 | 1.5" × 5.5" | 0.69 | Framing / structural lumber |
| 2×8 | 1.5" × 7.25" | 0.91 | Framing / structural lumber |
| 2×10 | 1.5" × 9.25" | 1.16 | Framing / structural lumber |
| 2×12 | 1.5" × 11.25" | 1.41 | Framing / structural lumber |
| 4/4 (≈1") | 1" × varies | — | Hardwood thickness; width varies |
| 8/4 (≈2") | 2" × varies | — | Hardwood thickness; width varies |
Hardwood thickness labels like 4/4 and 8/4 often have varying widths, so you usually calculate board feet with the formula.
Nominal vs actual size (more detail)
Dimensional lumber is commonly sold by a nominal name (like 2×4), but the real measured size is smaller after drying and planing. If you use the nominal size in the formula, your board feet estimate can be off.
If you are buying wood priced by board feet, always confirm which dimensions the seller uses for pricing.
Formula variants (quick comparison)
| When to use | Formula |
|---|---|
| All measurements in inches | BF = (T(in) × W(in) × L(in)) ÷ 144 |
| Length in feet (common) | BF = (T(in) × W(in) × L(ft)) ÷ 12 |
| Quick mental math | BF = (T(in) × W(in)) ÷ 12 × L(ft) |