Lumber Calculator Guide: Board Feet, Linear Feet & Project Costs (2026)

Board Feet vs Linear Feet: What's the Difference?

The two most common units for buying lumber are board feet and linear feet — and confusing them is one of the most expensive mistakes you can make at the lumber yard.

A linear footmeasures only length. One linear foot equals 12 inches, full stop. It says nothing about the board's thickness or width. Trim, molding, fascia boards, and decking are commonly sold by the linear foot because the cross-section is standard and what you're really buying is coverage.

A board footmeasures volume. It accounts for thickness, width, and length together. One board foot equals a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long — or any combination that equals the same volume. Hardwoods and structural lumber are typically priced per board foot.

To convert linear feet to board feet: multiply the linear footage by the thickness (inches) and width (inches), then divide by 12. A 2×6 board at 10 linear feet = (2 × 6 × 10) ÷ 12 = 10 board feet.

The Board Foot Formula

The formula is straightforward:

Board Feet = (Thickness × Width × Length) ÷ 12

Where thickness and width are in inches (use nominal dimensions) and length is in feet.

One important note: always use nominal dimensions(the labeled size like 2×4), not the actual measured dimensions, in this formula. The formula was designed around nominal sizes. According to the USDA Forest Service, this convention has been standard in the US lumber trade since the early 20th century.

Don't want to do the math by hand? Use our free lumber calculator to get instant board foot totals for any project.

Nominal vs Actual Lumber Dimensions

Here's a fact that surprises almost every first-time builder: a 2×4 is not 2 inches by 4 inches. It hasn't been since before most people alive today were born.

Nominal dimensions refer to the rough-sawn size of lumber before drying and planing. When a log is cut into a “2×4,” it initially is close to those dimensions. But drying shrinks the wood, and then the mill planes all four faces smooth, removing additional material. The result: actual dimensions are noticeably smaller.

Why does this matter? If you're building a wall with studs, the actual width of the wall will be 3.5 inches, not 4 inches. For a standard 2×4 wall with drywall on both sides, total wall thickness is about 4.5 inches. Plan your window and door rough openings accordingly.

Common Lumber Sizes and Their Uses

Not all lumber sizes are interchangeable. Each has a primary application in residential construction. Using the wrong size is either wasteful or structurally inadequate.

According to Random Lengths, a leading lumber price reporting service, 2×4 and 2×6 studs account for roughly 40% of all framing lumber volume sold in North America. Getting these sizes right is the single biggest variable in your lumber budget.

Top 5 Lumber Buying Tips to Save Money

Lumber prices are volatile. Random Lengths reported that framing lumber prices swung more than 300%between 2020 and 2023. You can't control the market, but you can shop smarter.

1. Always add a 10% waste factor

Cut-offs, defects you discover mid-project, measurement errors — they all add up. Order at least 10% more lumber than your calculations suggest. For complex projects with lots of angles (roof framing, stair stringers), bump that to 15%. Running out of lumber mid-project is almost always more expensive than buying a little extra upfront.

2. Buy from the same mill run when possible

Lumber from different mill runs can vary slightly in actual dimensions and moisture content. For finish work where boards sit next to each other — flooring, paneling, trim — buy everything from the same batch. Ask your lumber yard or big-box store to pull from the same unit/bundle.

3. Check every board before it leaves the store

Crowning (bow along the face), cupping (bow across the width), twisting, and checking (surface cracks) all reduce usable board length. Reject obviously warped boards before purchase. A warped 2×4 is impossible to frame straight and will cause you far more labor headaches than the $4 you saved by keeping it.

4. Use pressure-treated lumber for outdoor and ground-contact applications

Untreated lumber in contact with soil or moisture will rot within 2–5 years. Pressure-treated lumber costs 20–40% more upfront but lasts decades. The International Residential Code (IRC) requires pressure-treated lumber for all wood within 6 inches of grade and for ledger boards attached to the house. Skipping PT lumber to save money will cost significantly more in repairs.

5. Compare lumber yards vs big-box stores

Big-box stores (Home Depot, Lowe's) are convenient but not always the cheapest. Local lumber yards often have better prices on large quantities, better-quality boards (less warping), and knowledgeable staff. For projects requiring more than a few hundred board feet, call two or three local yards for quotes. The savings can be significant — especially for 2×6s, 2×8s, and pressure-treated material.

Lumber Grades Explained

Lumber is graded by appearance and structural properties. Understanding grades lets you pay for exactly what your project needs — no more, no less.

Structural framing grades(for dimensional lumber like 2×4, 2×6):

• Select Structural: Highest grade. Best strength properties, fewest knots. Used for headers, beams, and high-load applications.
• #1: High quality, few knots. Used in applications where strength and appearance both matter — exposed beams, visible framing.
• #2: Standard framing grade. The default for residential wall, floor, and roof framing. Balances cost and strength. This is what most homes are built with.
• #3: More knots and defects. Fine for blocking, bracing, and non-structural applications.
• Stud grade: Specifically graded for vertical stud applications. Not interchangeable with joist or rafter applications.

Appearance grades(for finish lumber like 1× boards):

• Clear / Select: Virtually knot-free. Used for paint-grade trim, furniture, and fine millwork. Most expensive.
• #1 Common: Small, tight knots. Good for stain-grade projects where a natural look is acceptable.
• #2 Common: Larger knots, some checks. Good for rustic applications, shelving, and projects where appearance is secondary.
• #3 Common: Significant defects. Economy boards for non-visible applications like subfloor blocking or temporary forms.

According to the American Lumber Standard Committee (ALSC), which oversees lumber grading standards in the US, approximately 70% of framing lumber sold in residential construction is #2 grade. Unless you have a specific structural or appearance requirement, start with #2 and upgrade only where needed.

Frequently Asked Questions

How do you calculate board feet of lumber?

Board feet = (thickness in inches × width in inches × length in feet) ÷ 12. For example, a 2×4 that is 8 feet long: (2 × 4 × 8) ÷ 12 = 5.33 board feet. A 1×6 at 10 feet: (1 × 6 × 10) ÷ 12 = 5 board feet. Use nominal dimensions (2×4, not actual 1.5×3.5) in this formula.

What is the difference between a board foot and a linear foot?

A linear foot measures only length — one linear foot is 12 inches regardless of the board's thickness or width. A board foot measures volume and accounts for all three dimensions. Trim, molding, and decking are often sold by the linear foot; structural lumber and hardwoods are typically sold by the board foot.

Why is a 2×4 actually 1.5 inches by 3.5 inches?

Nominal dimensions refer to the rough-sawn size before the wood is dried and planed smooth at the mill. Drying causes shrinkage, and planing removes additional material to create a smooth surface. The result: a 2×4 measures approximately 1.5 inches by 3.5 inches, and a 2×6 measures 1.5 inches by 5.5 inches.

How much lumber do I need for a 12×16 foot deck?

A 12×16 foot deck (192 sq ft) using 5/4×6 deck boards with 1/8-inch gaps requires approximately 195–200 linear feet of decking. Add 10% for waste and end cuts, bringing you to about 220 linear feet. You'll also need framing lumber: typically 2×8 or 2×10 joists on 16-inch centers, plus beams and posts. Always add at least 10% overage to your total lumber order.

What lumber grade should I use for framing?

#2 grade is the standard for most residential framing. It balances structural integrity and cost. #1 grade is used when appearance matters or in high-load applications. For non-structural applications like blocking, #3 or construction grade is fine. Select and appearance grades are reserved for finish work where the wood will be visible.

Should I use pressure-treated lumber for outdoor projects?

Yes — any lumber in ground contact or within 6 inches of the ground must be pressure-treated (PT) per most building codes. Deck joists, posts, and ledger boards should be PT. Above-ground decking can be PT, naturally durable species (cedar, redwood), or composite. PT lumber labeled UC4B or UC4C is rated for ground contact; UC3B is for above-ground outdoor use.