Lumber Calculator: Board Feet, Linear Feet & Dimensions
Lumber is sold by different units depending on the context: hardware stores price dimensional lumber (2×4s, 2×6s) by the linear foot, while sawmills and large wholesale orders use board feet. Knowing how to move between these units — and understanding the difference between nominal and actual dimensions — is essential for accurate material estimates and cost comparisons.
Understanding Lumber Measurement
Board foot (BF): The standard unit of lumber volume in the US. One board foot equals a piece 1 foot long, 1 foot wide, and 1 inch thick — 144 cubic inches. Board feet account for all three dimensions, making them ideal for comparing pieces of different sizes.
Linear foot: Simply a measure of length, ignoring width and thickness. A 2×4 stud sold at a home center is typically priced per linear foot. Two pieces of the same length but different cross-sections have the same linear footage but different board footage.
Nominal vs. actual dimensions: Lumber is named by its rough-sawn size before drying and surfacing. After the milling process the board is measurably smaller. A "2×4" actually measures 1½" × 3½". Always use actual dimensions when calculating board feet or planning joinery.
Board Foot Formula
Board Feet = (Thickness" × Width" × Length ft) ÷ 12
Example: 2" × 6" × 10 ft = 120 ÷ 12 = 10 BF
BF per linear foot = (T" × W") ÷ 12
Use nominal dimensions for ordering; use actual dimensions for joinery and fit.
Nominal vs. Actual Dimensions & Board Feet per Linear Foot
Board feet per linear foot (BF/LF) is calculated using nominal dimensions, which is the industry standard for ordering.
| Nominal Size | Actual Size | BF per Linear Foot | BF per 8-ft Board |
|---|---|---|---|
| 1×2 | ¾" × 1½" | 0.17 | 1.36 |
| 1×4 | ¾" × 3½" | 0.33 | 2.64 |
| 1×6 | ¾" × 5½" | 0.50 | 4.00 |
| 2×4 | 1½" × 3½" | 0.67 | 5.36 |
| 2×6 | 1½" × 5½" | 1.00 | 8.00 |
| 2×8 | 1½" × 7¼" | 1.33 | 10.64 |
| 2×10 | 1½" × 9¼" | 1.67 | 13.36 |
| 4×4 | 3½" × 3½" | 1.33 | 10.64 |
| 6×6 | 5½" × 5½" | 3.00 | 24.00 |
Related Conversion Tools
Frequently Asked Questions
What is a board foot?
A board foot is a unit of lumber volume equal to a piece 1 foot long, 1 foot wide, and 1 inch thick — 144 cubic inches. It is the standard unit for pricing and selling hardwood and large lumber orders in the United States.
How do I calculate board feet for a project?
Use the formula: Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12. For example, a board that is 2 inches thick, 6 inches wide, and 10 feet long contains (2 × 6 × 10) ÷ 12 = 10 board feet.
Why do lumber nominal and actual dimensions differ?
Nominal dimensions refer to the rough-sawn size before drying and planing. After the milling process removes moisture and smooths the surface, the board is smaller than its stated size. A "2×4" is called that because it was once 2 inches by 4 inches when freshly cut; after drying and planing it measures 1.5 inches by 3.5 inches.