Lumber Calculator
Calculate board feet and estimate lumber costs.
This tool is for informational and educational purposes only. It is not a substitute for professional financial, medical, legal, or engineering advice. See Terms of Service.
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This calculator computes board feet for any dimensional lumber and optionally estimates your total material cost. Here is how to get an accurate result:
- Choose your lumber size. Select a common nominal size from the dropdown (2x4, 2x6, 2x8, 2x10, 2x12, or 4x4), or choose "Custom dimensions" to enter any thickness and width. The thickness and width fields will populate automatically when you pick a preset.
- Decide on nominal vs. actual dimensions. The "Use actual dimensions" checkbox is on by default. Actual dimensions are smaller than nominal: a 2x4 is actually 1.5 inches by 3.5 inches. Board feet calculations using actual dimensions give you the true volume of wood you are buying. Uncheck this box if your supplier prices by nominal board feet, which is common for rough-sawn lumber.
- Enter length and quantity. Length is the length of each individual board in feet. Quantity is how many boards you need. The calculator multiplies board feet per piece by quantity for your total.
- Enter an optional price. If you know the cost per board foot at your local supplier, enter it and the calculator will show your estimated total material cost. Leave it blank if you only need the board-foot count.
Results update live as you type. Use the Share button to send your inputs to a co-worker or supplier, or Copy to paste the total into a quote or spreadsheet.
About Board Feet
A board foot is the standard unit for measuring lumber volume in North America. One board foot equals a piece of wood that is 1 inch thick, 12 inches wide, and 12 inches long, which is equivalent to 144 cubic inches or 1/12 of a cubic foot. The formula is straightforward: multiply thickness in inches by width in inches by length in feet, then divide by 12.
This unit matters because lumber pricing at most lumber yards and home centers is quoted per board foot, not by the linear foot. Two boards of the same length but different widths will cost different amounts because they contain different volumes of wood. Knowing your board-foot total lets you compare prices across suppliers and avoid under-ordering or over-ordering.
One important distinction: nominal dimensions are the traditional names given to lumber sizes before they are dried and surfaced. A "2x4" starts as a rough-sawn 2-inch by 4-inch board, but after kiln drying and planing it measures 1.5 inches by 3.5 inches. When buying surfaced lumber (what you find at a standard home center), you are paying for the actual volume. Use actual dimensions for the most accurate board-foot calculation.
Frequently Asked Questions
How many board feet are in a 2x4 that is 8 feet long?
Using nominal dimensions: (2 x 4 x 8) / 12 = 5.33 board feet. Using actual dimensions (1.5 x 3.5): (1.5 x 3.5 x 8) / 12 = 3.5 board feet. Most retail lumber is priced by actual board feet, so a 2x4x8 typically contains 3.5 board feet. Rough-sawn lumber from a sawmill may be sold at the nominal 5.33 board feet. Always confirm with your supplier which method they use.
What is the actual size of common dimensional lumber?
Dimensional lumber sold at home centers is surfaced and dried, making it smaller than its nominal name suggests. Common actual sizes: a 2x4 is 1.5" x 3.5", a 2x6 is 1.5" x 5.5", a 2x8 is 1.5" x 7.25", a 2x10 is 1.5" x 9.25", a 2x12 is 1.5" x 11.25", and a 4x4 is 3.5" x 3.5". The thickness settles at 1.5 inches for all standard 2-by lumber. Width shrinks proportionally more for wider boards due to the greater surface area being planed.
How do I calculate how much lumber I need for a project?
Start by listing every board in your project with its size and length. Calculate the board feet for each distinct board type using this calculator, then add a 10-15% waste allowance for cuts, defects, and mistakes. Group boards by size and length when buying, since longer boards can often be cut down and are sometimes cheaper per board foot than shorter pieces. For large framing projects, it also helps to calculate linear feet separately, since structural lumber like framing studs is often sold by the linear foot at fixed lengths (8, 10, 12, 16, and 20 feet).
What is a typical price per board foot for lumber?
Lumber prices vary significantly by species, grade, region, and market conditions. As a rough reference, construction-grade framing lumber (SPF or Hem-Fir 2x4s) typically ranges from $0.50 to $1.00 per board foot at large home centers. Higher grades and wider boards cost more per board foot. Hardwoods like oak, maple, and walnut range from $3 to $10 or more per board foot depending on the species and grade. Cedar and redwood fall between framing lumber and hardwoods. Always check your local supplier for current pricing, as lumber markets can shift substantially.
What is the difference between board feet and linear feet?
Linear feet simply measures length, with no regard for thickness or width. It is useful when you need to know the total run of material, such as the length of baseboard molding or the total span of fence rails. Board feet measure volume: they account for thickness and width as well as length. Board feet are used when comparing lumber costs across different sizes or when estimating the total volume of wood in a project. Some suppliers price standard-size trim and molding by the linear foot, while structural and finish lumber is typically priced by the board foot.