Board Foot Calculator – Calculate Lumber by Board Feet

What Is a Board Foot?

A board foot is the standard unit of lumber measurement in the United States and Canada. One board foot equals the volume of a piece of wood that measures 1 inch thick × 12 inches wide × 12 inches long — equivalent to 144 cubic inches or 1/12 of a cubic foot.

The formula for board feet is: Board Feet = (Thickness (in) × Width (in) × Length (ft)) ÷ 12.

This simple formula applies whether you're buying rough lumber at a sawmill, ordering hardwood from a specialty dealer, or calculating the yield from a log. The board foot accounts for volume rather than just length, which is why a 2×4 and a 2×8 of the same length are priced differently despite being cut from the same tree.

Example: A board 1.5 inches thick × 5.5 inches wide × 8 feet long → (1.5 × 5.5 × 8) ÷ 12 = 66 ÷ 12 = 5.5 board feet.

Note: Lumber dimensions are stated as nominal (rough-cut) sizes, not actual sizes. A "2×4" actually measures 1.5 inches × 3.5 inches when surfaced (S4S). For board foot calculations, use the nominal dimensions — this is the industry convention used by all lumber suppliers when quoting prices.

Nominal vs. Actual Lumber Dimensions

One of the most confusing aspects of lumber buying is that the name of the board and its actual measured size are different. This is because lumber is sold by its rough-cut (green) dimensions, but you receive it after it has been dried and surfaced (planed smooth).

Important: When buying dimensional lumber (2×4s, 2×6s) at a big-box store like Home Depot or Lowe's, pricing is typically per linear foot (by the piece), not by the board foot. Board foot pricing is more common at sawmills, hardwood dealers, and specialty lumberyards where custom-sized rough lumber is sold.

Board Feet for Common Wood Species

The board foot unit is the same regardless of species, but pricing per board foot varies dramatically based on species rarity, grade, and market conditions. Here's a general price guide for popular species in the US market:

Prices vary by region, grade, and current market conditions. Lumber prices can swing 50–100% within a year based on housing demand and supply chain factors. Buying direct from a local sawmill — especially for common domestic species — can save 30–50% compared to retail lumber dealers.

Lumber Grades and Their Impact on Board Feet

Lumber grading affects both price and usable yield. When you buy lower-grade lumber, you pay less per board foot but may waste a higher percentage due to knots, checks, and other defects that must be cut around.

Hardwood grades (NHLA standards):

• FAS (Firsts and Seconds): Highest grade. Minimum 83% clear cuttings from each face. Premium price, minimal waste.
• Select: One good face, similar to FAS from one side. Good for furniture fronts.
• No. 1 Common: Minimum 66% clear cuttings. Good value for smaller projects — enough clear wood for most furniture parts.
• No. 2 Common: Minimum 50% clear cuttings. Significantly cheaper, but substantial waste. Good for rustic projects or painted work.
• No. 3 Common: Minimum 33% clear cuttings. Very inexpensive, best for boxes, utility work, and painted applications.

For woodworking projects where you need clear, knot-free material, buy FAS or Select and use the full board feet — your waste factor is low. For painted furniture or utility projects, No. 1 or No. 2 Common can cut your material costs in half, but factor in 25–40% waste when calculating how many board feet to buy.

How to Use Board Foot Calculations for Projects

Planning a woodworking project requires converting your cut list (the specific pieces you need) into total board feet for ordering. Here's a systematic approach:

Step 1: Create a cut list. List every piece in your project with its finished thickness, width, and length.

Step 2: Add milling allowances. Rough lumber needs to be milled to finished dimensions. Add ¼" to ½" in both thickness and width to account for jointing, planing, and straightening.

Step 3: Calculate board feet per piece. (Rough thickness × Rough width × Length in feet) ÷ 12

Step 4: Sum all pieces. Add the board feet for every piece in your cut list.

Step 5: Add waste factor. Add 20–30% for a hardwood project (for grain matching, defect avoidance, and cutting errors). New woodworkers should add 35–40%.

Example project — a small coffee table:

Buying Lumber: Tips to Get the Best Value

Whether you're a hobbyist woodworker or a professional contractor, buying lumber efficiently saves money and reduces waste:

• Buy longer boards when possible. Long boards offer more flexibility for laying out parts efficiently to work around defects. A single 10-foot board often yields more usable material than two 5-foot boards of the same total length.
• Visit the lumber yard in person. Online orders are convenient but you can't select specific boards. For hardwoods, hand-picking at the yard lets you reject twisted, cupped, or defect-heavy boards that waste your money.
• Buy a bit more than you think you need. It's far worse to run out of matching wood mid-project than to have a few extra board feet. Species and grades vary batch to batch — future orders may not match.
• Consider rough lumber for large projects. Rough sawn lumber from a sawmill is typically 30–50% cheaper than S4S (surfaced 4 sides) from a retail lumber dealer. If you have or can rent a planer and jointer, buying rough saves significantly on large projects.
• Check moisture content. Green or partially dried lumber will warp and shrink after you cut it. Kiln-dried (KD) lumber should have moisture content below 8% for interior furniture. Ask for a moisture reading or bring a meter.
• Stack and sticker your lumber. If lumber arrives before you're ready to use it, stack it flat with small strips (stickers) between each layer to allow air circulation and prevent warping.