Board Foot Calculator

How to Use This Board Foot Calculator

Using this board foot calculator is straightforward. Start by selecting your lumber thickness using the quarter system dropdown — choose from common sizes like 4/4 (1 inch), 6/4 (1.5 inches), or 8/4 (2 inches), or enter a custom thickness for specialty lumber. Then enter the width in inches and length in feet of your board.

If you have multiple boards with the same dimensions, adjust the quantity slider. The calculator instantly shows board feet per piece and total board feet. Need to budget your project? Check the "Include price estimate" box, enter the price per board foot for your wood species, and you'll see the total estimated cost.

All calculations update in real time as you change any value — no need to press a button. The formula used is the standard lumber industry calculation: Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12.

What Is a Board Foot? A Woodworker's Guide to Buying Lumber

If you've ever walked into a hardwood lumberyard and seen prices like "$5.25/BF," you've encountered the board foot — the standard unit of measurement for hardwood lumber. Understanding board feet is essential for any woodworker, whether you're building furniture, installing hardwood flooring, or crafting cabinets. This guide covers everything you need to know about calculating board feet, reading lumber thickness grades, and avoiding costly mistakes when buying lumber.

What Is a Board Foot?

A board foot (BF) is a unit of volume equal to 144 cubic inches of wood. Imagine a board that is exactly 1 inch thick, 12 inches wide, and 12 inches long — that's one board foot. The formula is simple: multiply thickness (inches) × width (inches) × length (feet), then divide by 12.

Why do lumberyards use board feet rather than linear feet? Because hardwood boards come in random widths and lengths, and pricing by volume ensures you pay for the actual amount of wood, not just the length. A wide 12-inch board contains the same wood as two 6-inch boards of the same thickness and length, and board-foot pricing reflects this naturally.

Understanding the Quarter System (4/4, 5/4, 6/4, 8/4)

Hardwood thickness is labeled using the quarter system, which refers to rough-sawn thickness before surfacing:

• 4/4 (four-quarter) = 1 inch rough, typically 3/4" to 7/8" after surfacing. The most common thickness for furniture making.
• 5/4 (five-quarter) = 1-1/4 inch rough, finishes to about 1-1/16". Often used for deck boards and stair treads.
• 6/4 (six-quarter) = 1-1/2 inch rough, finishes to about 1-1/4". Good for table legs and thicker components.
• 8/4 (eight-quarter) = 2 inch rough, finishes to about 1-3/4". Used for table tops, workbench tops, and lathe turning blanks.
• 12/4 (twelve-quarter) = 3 inch rough. For large architectural work, mantels, and heavy furniture.

When calculating board feet, you always use the rough-sawn thickness, not the finished thickness. A board labeled 4/4 that finishes to 3/4" is still calculated as 1 inch thick for board-foot pricing. This accounts for the wood lost during surfacing and planing.

Rough vs. Surfaced Lumber

Lumber is typically sold in one of three surface conditions:

• Rough (RGH): Straight from the sawmill, no surfacing. You'll need a jointer and planer to prepare it. Cheapest per board foot.
• S2S (Surfaced Two Sides): The two faces are planed smooth, but edges are still rough. You'll need to rip one straight edge on a table saw.
• S4S (Surfaced Four Sides): All four sides surfaced smooth and square. Ready to use but most expensive per board foot — you're paying for the milling labor.

A 4/4 board that is S2S will finish to roughly 13/16", while S4S may go down to 3/4". Despite this, you're paying for the board feet calculated from the original rough thickness. This is why many serious woodworkers invest in a jointer and planer — the savings from buying rough lumber add up quickly.

Common Hardwood Board Foot Prices (2025)

Prices vary significantly by region, grade, and availability, but here are rough estimates for FAS (First and Second) grade lumber in the continental US:

• Red Oak: $3.50–$6.00 / BF — the most common and affordable hardwood.
• Hard Maple: $4.50–$7.50 / BF — dense and durable, great for cutting boards and furniture.
• Cherry: $5.00–$8.50 / BF — rich color that darkens beautifully with age.
• Walnut: $8.00–$14.00 / BF — premium furniture wood with stunning dark grain.
• White Oak: $5.50–$9.00 / BF — weather-resistant, ideal for outdoor and mission-style furniture.
• Ash: $3.00–$5.50 / BF — excellent for bending and tool handles.
• Mahogany (Genuine): $12.00–$25.00 / BF — premium imported hardwood for fine furniture.

5 Mistakes to Avoid When Buying Lumber

1. Confusing linear feet with board feet: A 1×12×8' board contains 8 board feet; a 1×6×8' board contains 4 board feet. Same linear length, half the wood volume. Always calculate board feet before comparing prices.
2. Not accounting for waste: Add 20-30% extra to your calculated board footage for defects, knots, checks, and cutting waste. A 10-board-foot project realistically needs 12-13 board feet of rough lumber.
3. Buying S4S when you don't need it: If you have or can access a planer and jointer, buying rough or S2S lumber can save 30-50% per board foot. The tools pay for themselves after a few projects.
4. Not inspecting boards individually: When buying from a lumberyard, you typically pick boards yourself. Look for excessive cupping, twisting, large knots on the edges, and end checks. Don't just take the top board from the stack.
5. Ignoring moisture content: Kiln-dried lumber (6-8% moisture content) is what you want for indoor furniture. Air-dried (12-15%) needs further drying before use. Green lumber (above 19%) is for outdoor construction only. Always ask.

Quick Reference: Board Feet in Common Boards

Here's a handy reference table for quick estimation: