Board Foot Calculator
Board Foot Calculator: How to Calculate Board Feet for Lumber, Logs, and Projects
If you’ve ever tried to buy hardwood lumber, rough-sawn timber, or price out a woodworking project, you’ve run into board feet. It’s the standard unit of measurement for lumber volume in the United States and Canada — and once you understand it, calculating board footage for any piece of wood takes about ten seconds.
This guide covers the board foot formula, worked examples for common lumber dimensions, a ready-reference table for standard sizes, and how board feet apply to logs, spray foam, and pricing.
What Is a Board Foot?
A board foot is a unit of volume equal to a piece of wood that is 1 foot long × 1 foot wide × 1 inch thick. In cubic terms, that’s 144 cubic inches or 1/12 of a cubic foot.
The key thing that confuses people: board feet measure volume, not area. Two boards that cover the same floor area can have completely different board footage if their thicknesses differ.
Board feet are the standard unit for buying and selling hardwood lumber, rough-sawn timber, live-edge slabs, and specialty wood. Softwood dimensional lumber (the 2×4s at a home center) is typically sold by the linear foot — but hardwoods at sawmills and specialty lumber yards are almost universally priced per board foot (BF).
The Board Foot Formula
The formula for calculating board feet is:
Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12
Or, if all dimensions are in inches:
Board Feet = (Thickness × Width × Length in inches) ÷ 144
That division by 12 (or 144) is the only conversion needed. Thickness and width are measured in inches; length is measured in feet.
Step-by-Step Example
You have a board that is 1.25 inches thick, 8 inches wide, and 6 feet long.
Board Feet = (1.25 × 8 × 6) ÷ 12 = 60 ÷ 12 = 5 board feet
If you buy 4 of those boards: 4 × 5 = 20 board feet total
At $6.00 per board foot: 20 × $6.00 = $120.00
Nominal vs. Actual Lumber Dimensions
This is the most important practical detail every woodworker and builder needs to know. Standard dimensional lumber — the 2×4s, 2×6s, and 1×12s sold at lumber yards — has nominal dimensions (what it’s called) that are larger than its actual measured dimensions (what you actually receive).
Nominal vs. Actual Size Reference Table
| Nominal Size | Actual Size (Dry) |
|---|---|
| 1×2 | 0.75″ × 1.5″ |
| 1×3 | 0.75″ × 2.5″ |
| 1×4 | 0.75″ × 3.5″ |
| 1×6 | 0.75″ × 5.5″ |
| 1×8 | 0.75″ × 7.25″ |
| 1×10 | 0.75″ × 9.25″ |
| 1×12 | 0.75″ × 11.25″ |
| 2×2 | 1.5″ × 1.5″ |
| 2×4 | 1.5″ × 3.5″ |
| 2×6 | 1.5″ × 5.5″ |
| 2×8 | 1.5″ × 7.25″ |
| 2×10 | 1.5″ × 9.25″ |
| 2×12 | 1.5″ × 11.25″ |
| 4×4 | 3.5″ × 3.5″ |
| 6×6 | 5.5″ × 5.5″ |
| 8×8 | 7.5″ × 7.5″ |
For board foot calculations of softwood lumber, most suppliers use the nominal dimensions, not the actual. For hardwood, thickness is measured in the actual rough-sawn dimension (expressed in quarter-inches: 4/4, 5/4, 6/4, 8/4, etc.), and the actual measured width and length are used.
Is a 10 ft 2×4 Actually 10 ft?
Yes — length is the one dimension that is accurate on dimensional lumber. A 10-foot 2×4 is actually 10 feet long (sometimes fractionally over to allow for end trimming). The dimensional shortfall only applies to thickness and width, which are reduced during drying and surfacing after milling.
So a 2×4×10 is actually 1.5″ thick × 3.5″ wide × 10 feet long.
Common Lumber Board Feet Reference Table
Use this table to instantly look up board footage for the most common lumber sizes without manual calculation. These use nominal dimensions as is standard for softwood.
Board Feet by Lumber Size and Length
| Board Size | 6 ft | 8 ft | 10 ft | 12 ft | 16 ft |
|---|---|---|---|---|---|
| 1×4 | 2.00 BF | 2.67 BF | 3.33 BF | 4.00 BF | 5.33 BF |
| 1×6 | 3.00 BF | 4.00 BF | 5.00 BF | 6.00 BF | 8.00 BF |
| 1×8 | 4.00 BF | 5.33 BF | 6.67 BF | 8.00 BF | 10.67 BF |
| 1×10 | 5.00 BF | 6.67 BF | 8.33 BF | 10.00 BF | 13.33 BF |
| 1×12 | 6.00 BF | 8.00 BF | 10.00 BF | 12.00 BF | 16.00 BF |
| 2×4 | 4.00 BF | 5.33 BF | 6.67 BF | 8.00 BF | 10.67 BF |
| 2×6 | 6.00 BF | 8.00 BF | 10.00 BF | 12.00 BF | 16.00 BF |
| 2×8 | 8.00 BF | 10.67 BF | 13.33 BF | 16.00 BF | 21.33 BF |
| 2×10 | 10.00 BF | 13.33 BF | 16.67 BF | 20.00 BF | 26.67 BF |
| 2×12 | 12.00 BF | 16.00 BF | 20.00 BF | 24.00 BF | 32.00 BF |
| 4×4 | 8.00 BF | 10.67 BF | 13.33 BF | 16.00 BF | 21.33 BF |
| 4×6 | 12.00 BF | 16.00 BF | 20.00 BF | 24.00 BF | 32.00 BF |
| 6×6 | 18.00 BF | 24.00 BF | 30.00 BF | 36.00 BF | 48.00 BF |
| 8×8 | 32.00 BF | 42.67 BF | 53.33 BF | 64.00 BF | 85.33 BF |
Hardwood Quarter-Sizing: How Hardwood Thickness Works
When you buy hardwood at a specialty lumber yard or sawmill, thickness is expressed in quarters of an inch rather than nominal inches. This is the NHLA (National Hardwood Lumber Association) standard.
| Quarter Size | Thickness |
|---|---|
| 4/4 | 1 inch |
| 5/4 | 1.25 inches |
| 6/4 | 1.5 inches |
| 8/4 | 2 inches |
| 10/4 | 2.5 inches |
| 12/4 | 3 inches |
| 16/4 | 4 inches |
These are rough-sawn nominal thicknesses. After surfacing on two sides (S2S), you typically lose 3/16″ to 1/4″ per face. A 4/4 board surfaced S2S comes out to approximately 13/16″ to 7/8″ actual thickness.
For board foot calculations, always use the nominal rough-sawn thickness — that’s what the lumber was priced and tallied at before surfacing.
Board Foot Price Calculator: How Much Does a Board Foot Cost?
Board foot pricing depends on wood species, grade, thickness, and current market conditions. Here are current general price ranges:
Average Price per Board Foot by Species
| Wood Species | Price per Board Foot (approx.) |
|---|---|
| Construction pine (softwood) | $1.00 – $2.50 |
| Poplar | $3.00 – $5.00 |
| Hard maple | $5.00 – $9.00 |
| Red oak | $4.00 – $7.00 |
| White oak | $5.00 – $9.00 |
| Cherry | $6.00 – $12.00 |
| Black walnut | $8.00 – $18.00 |
| White ash | $4.00 – $7.00 |
| Hickory | $4.00 – $8.00 |
| Teak | $20.00 – $40.00 |
| Purpleheart (exotic) | $12.00 – $25.00 |
Total project cost formula: Total BF needed × Price per BF = Material cost
Example: A table top requiring 40 board feet of black walnut at $12/BF: 40 × $12 = $480 in material
What Is MBF?
MBF stands for thousand board feet — used for large commercial lumber orders. 1 MBF = 1,000 board feet. If walnut is quoted at $1,200/MBF, that’s $1.20 per board foot.
Board Feet for Spray Foam Insulation
Board feet have a second major use in construction: measuring spray foam insulation. In this context, a board foot of spray foam is a volume that covers 1 square foot of area at 1 inch thick — identical to the lumber definition.
How to Calculate Board Feet for Spray Foam
Board Feet of Foam = Area (sq ft) × Thickness (inches)
Example: Insulating a wall cavity that is 200 sq ft at 3.5 inches thick (standard 2×4 stud bay): 200 × 3.5 = 700 board feet of spray foam
Spray foam is sold in kits rated by board feet coverage. A 200 BF kit, a 600 BF kit, and a 1,500 BF kit are common sizes. Always check the manufacturer’s yield rating, as actual output varies with temperature and application technique. Adding 10–15% overage is standard practice.
Log Board Foot Calculator: The Doyle Rule
For timber buyers, foresters, and sawmill operators, log board footage estimates how much usable lumber can be sawn from a given log. The most widely used method in the eastern US is the Doyle Log Rule:
Board Feet (Doyle) = ((Diameter – 4) ÷ 4)² × Length
Where diameter is the small-end diameter in inches (not including bark), and length is in feet.
Example: A log with a 12-inch small-end diameter and 16-foot length: ((12 – 4) ÷ 4)² × 16 = (2)² × 16 = 4 × 16 = 64 board feet
Log Board Feet Quick Reference (Doyle Rule)
| Small-End Diameter | 8 ft log | 12 ft log | 16 ft log |
|---|---|---|---|
| 8 inches | 16 BF | 24 BF | 32 BF |
| 10 inches | 36 BF | 54 BF | 72 BF |
| 12 inches | 64 BF | 96 BF | 128 BF |
| 14 inches | 100 BF | 150 BF | 200 BF |
| 16 inches | 144 BF | 216 BF | 288 BF |
| 18 inches | 196 BF | 294 BF | 392 BF |
Note: The Doyle Rule tends to underestimate yield on small logs (under 12 inches) and overestimate on very large logs. The International 1/4-inch Rule is more accurate, but the Doyle Rule remains the most commonly used in the US South and Midwest.
Square Feet vs. Board Feet: What’s the Difference?
This confusion comes up constantly. The short version:
- Square feet measure area (length × width, no thickness)
- Board feet measure volume (length × width × thickness)
A single board foot equals 1 square foot of surface area at 1 inch thick. A 1×12×16 board (1 inch thick × 12 inches wide × 16 feet long) contains 16 board feet and also covers 16 square feet of surface — but only because the thickness is exactly 1 inch.
Converting Square Feet to Board Feet
Board Feet = Square Feet × Thickness in Inches
If your project requires coverage of 100 sq ft with 2-inch thick lumber: 100 × 2 = 200 board feet
Frequently Asked Questions
How Do I Calculate a Board Foot?
Multiply the thickness in inches × the width in inches × the length in feet, then divide by 12. The formula is: BF = (T” × W” × L’) ÷ 12. For all measurements in inches, divide by 144 instead. Always use nominal (rough-sawn) dimensions for hardwood, and nominal listed dimensions for dimensional softwood.
How Many Board Feet Is a 2×4×8?
Using nominal dimensions (2″ × 4″ × 8′): (2 × 4 × 8) ÷ 12 = 64 ÷ 12 = 5.33 board feet
A 2×4×10 = 6.67 BF. A 2×4×12 = 8 BF. A 2×4×16 = 10.67 BF.
How to Calculate Board Feet for Spray Foam?
Board feet of spray foam = Area in square feet × Desired thickness in inches. For a 200 sq ft ceiling sprayed at 2 inches deep, you need 200 × 2 = 400 board feet of spray foam. Check your product kit’s rated yield and add 10–15% for overage due to temperature variation and application technique.
Are There Board Foot Calculators Online?
Yes — our board foot calculator at the top of this page lets you enter thickness, width, length, and number of pieces to get total board footage and material cost instantly. It handles both decimal and fractional dimensions and is free to use for any project.
Is a 10 ft 2×4 Actually 10 ft?
Yes — the length of dimensional lumber is accurate. A 10-foot 2×4 is genuinely 10 feet long (120 inches). The “nominal” dimension discrepancy only affects thickness and width: a 2×4 is actually 1.5 inches thick by 3.5 inches wide after drying and surfacing, not 2 by 4.
How Many Board Feet Are in a 2×6×10?
Using nominal dimensions (2″ × 6″ × 10′): (2 × 6 × 10) ÷ 12 = 120 ÷ 12 = 10 board feet
Quick Reference Summary
| Formula | Board Feet = (T” × W” × L’) ÷ 12 |
|---|---|
| 1 board foot equals | 144 cubic inches / 1/12 cubic foot |
| MBF | 1,000 board feet |
| 2×4×8 | 5.33 BF |
| 2×4×10 | 6.67 BF |
| 2×6×10 | 10 BF |
| 2×6×12 | 12 BF |
| Spray foam board foot | 1 sq ft × 1 inch thick |
| Doyle log rule | ((D–4)÷4)² × Length |
| Softwood uses | Nominal dimensions |
| Hardwood uses | Actual rough-sawn dimensions |
Use the board foot calculator above to calculate any lumber order in seconds — enter your dimensions, quantity, and price per board foot to get total footage and material cost instantly.