How to Calculate Board Feet of Lumber: Formula, Examples & Calculator
A board foot is a unit of lumber volume equal to 144 cubic inches — the equivalent of a piece of wood 12 inches long, 12 inches wide, and 1 inch thick. The formula is: Thickness (in) × Width (in) × Length (ft) A 12. This guide covers both formulas, worked examples, nominal vs actual dimensions, and how to price a lumber order for any project in the US.
Board Feet = Thickness (in) × Width (in) × Length (ft) A 12
Example: 2 in × 8 in × 10 ft / 12 = 13.33 board feet
All measurements in inches? Divide by 144 instead of 12.
What Is a Board Foot?
A board foot is a volume measurement, not a surface area or length measurement. One board foot equals 144 cubic inches — roughly one square foot of wood that is 1 inch thick.
The term is used by hardwood dealers, sawmills, woodworkers, and lumber suppliers across the United States. A supplier in Portland, Oregon may price rough hardwood by the board foot, while a home-improvement store in Dallas, Texas may sell standard construction lumber by the piece or by the linear foot. Knowing how to calculate board feet lets you compare pricing across suppliers and estimate the true cost of any lumber order.
Board Foot Formula
There are two versions depending on how you measure length.
When length is in feet (most common)
When all measurements are in inches
The divisor changes from 12 to 144 because one board foot contains 144 cubic inches. Both formulas give identical results — use whichever matches your measurements.
Example 1: One Lumber Board
A single board with these dimensions:
- Thickness: 2 inches
- Width: 8 inches
- Length: 10 feet
Pricing the board
If the lumber costs $6.00 per board foot:
The estimated cost is approximately $79.98, before taxes, delivery, or supplier-specific charges.
Example 2: Multiple Boards
You need six boards, each measuring 1 inch thick, 6 inches wide, and 8 feet long.
Step 1: Calculate one board
Step 2: Multiply by quantity
This approach lets you compare lumber costs between suppliers in cities such as Cleveland, Pittsburgh, Indianapolis, or Kansas City — simply multiply the total board feet by each supplier's price per board foot.
Using the all-inches formula
If the same board's length is given as 96 inches instead of 8 feet:
Same answer, different divisor — because 96 in / 12 = 8 ft.
Nominal vs Actual Lumber Dimensions
One of the most common pricing errors comes from using the size printed on a lumber label rather than the board's actual dimensions.
| Nominal Size | Actual Size (approx.) | Board Feet (10 ft, nominal) | Board Feet (10 ft, actual) |
|---|---|---|---|
| 1 × 4 | 0.75 in × 3.5 in | 3.33 bf | 2.19 bf |
| 1 × 6 | 0.75 in × 5.5 in | 5.00 bf | 3.44 bf |
| 2 × 4 | 1.5 in × 3.5 in | 6.67 bf | 4.38 bf |
| 2 × 6 | 1.5 in × 5.5 in | 10.00 bf | 6.88 bf |
| 2 × 8 | 1.5 in × 7.25 in | 13.33 bf | 9.06 bf |
| 4 × 4 | 3.5 in × 3.5 in | 13.33 bf | 10.21 bf |
Board Feet vs Square Feet vs Linear Feet
These three measurements are frequently confused, but they describe completely different things.
| Measurement | What It Measures | Common Use |
|---|---|---|
| Board feet | Lumber volume (T × W × L) | Hardwood pricing, sawmill sales, woodworking |
| Square feet | Surface area (L × W) | Flooring, walls, countertops, paneling |
| Linear feet | Length only | Trim, molding, fencing, long boards |
A board's square footage does not equal its board footage unless you also know its thickness. A 2-inch thick board has twice the board feet of a 1-inch board with the same face dimensions.
Should You Add Extra Lumber?
For most projects, order more lumber than the calculated board feet. The right amount depends on the project type and lumber quality.
| Project Type | Suggested Extra | Why |
|---|---|---|
| Simple framing / dimensional lumber | 5–10% | Cuts, cracked ends, minor warping |
| Decking | 10–15% | Spacing, end trimming, crown cuts |
| Hardwood flooring | 10–15% | Pattern matching, grading defects |
| Custom cabinetry / fine woodworking | 15–20% | High-grade selection, figure matching, errors |
| Rough-sawn hardwood | 15–25% | Defects, checks, unusable sections |
This waste allowance is calculated on top of the board-foot total, separate from the formula itself. Always confirm the final quantity with your lumber dealer or contractor.
Calculate Board Feet Instantly
Use the AmericaCalculator Board Foot Calculator to estimate lumber for decks, furniture, framing, cabinets, or any woodworking project.
Common Board Foot Mistakes
- Dividing by 12 when length is in inches (should divide by 144).
- Using nominal dimensions when the supplier prices by actual dimensions, or vice versa.
- Forgetting to multiply the per-board result by the number of boards in the order.
- Confusing board feet (volume) with square feet (area) or linear feet (length).
- Not adding a waste allowance before placing the lumber order.
- Assuming all suppliers measure the same way — always confirm the measurement standard.
Frequently Asked Questions
Formula: T × W × L / 12 = Board Feet
Related Articles & Calculators
- Board Foot Calculator — calculate board feet instantly without doing the math
- How to Calculate Square Feet of a Room — for flooring and surface area estimates
- How to Calculate Square Footage of a Building — for framing and whole-building material estimates
- How to Calculate Roof Square Footage — pitch factors and roofing material estimates
- Concrete Calculator — estimate concrete for foundations, slabs, and footings
- Cubic Yard Calculator — convert volume for bulk material orders
Disclaimer: This article is for general educational purposes. Lumber dimensions, grading practices, pricing methods, and acceptable measurement standards can vary by supplier and project. Confirm final quantities with your lumber dealer, contractor, or project plans.