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Board Foot Calculator: How to Figure Lumber

Updated · Standard formula, shown below

Board feet 4.00 bd ft
Cost at $4/bd ft
16.00 $
Result
Thickness
1 in
You entered
Width
6 in
You entered

Board Foot Calculator: How to Figure Lumber

A board foot calculator works out the volume of lumber in board feet—the standard unit for buying rough-sawn wood in North America. You enter the thickness, width, and length of a board, and the calculator returns the number of board feet, which you multiply by the price per board foot to get the cost.

Formula

The board foot formula is simple: Board Feet = (Thickness in inches × Width in inches × Length in feet) ÷ 12. A single board foot equals a piece 12 inches wide, 12 inches long, and 1 inch thick—that’s 144 cubic inches. The division by 12 converts the length from feet into inches so all three dimensions share the same unit.

Variables:

  • T = thickness in inches (in)
  • W = width in inches (in)
  • L = length in feet (ft)

If your length is in inches, use Board Feet = (T × W × L in inches) ÷ 144 instead. Both formulas give the same result because 12 inches × 12 inches × 1 inch = 144 cubic inches.

Worked Example

Using the calculator defaults: a board 1 inch thick, 6 inches wide, and 8 feet long.

  1. Multiply thickness × width × length: 1 × 6 × 8 = 48
  2. Divide by 12: 48 ÷ 12 = 4
  3. Result: 4 board feet

At $4 per board foot, that board costs $16. The calculator shows the same: 4.00 board feet and $16.00.

When to Use Board Feet

Board feet are used for rough, unfinished lumber—the kind sold at sawmills and hardwood dealers. If you buy surfaced (planed) wood like S4S (surfaced on four sides) from a home center, it’s usually priced per linear foot, not per board foot. Board feet apply when you’re buying hardwood for furniture, cabinetry, or any project where you’ll do your own milling.

Typical uses:

  • Estimating how much lumber a table, cabinet, or shelf needs
  • Comparing prices between different thicknesses and widths
  • Calculating waste when you buy more than the finished dimensions
  • Ordering from a mill that sells by the board foot

How to Read the Result

The board foot count tells you the nominal volume of the wood. If you buy 100 board feet, you’re paying for the volume of the rough lumber. After planing and cutting, you’ll lose some to saw kerf and surface smoothing—typically 10–20% for surfaced wood. So if a project needs 50 board feet of finished parts, order 55–60 board feet to cover waste.

Price is usually quoted per board foot, so multiply the board feet by that price. Some dealers add a surcharge for wider or longer boards, but the base calculation stays the same.

Common Mistakes and Misconceptions

The biggest error is mixing units. If you measure length in inches but forget to divide by 144, you’ll get a number 12 times too large. Another common mistake is using the finished dimensions instead of the rough dimensions. A 1-inch-thick board that’s planed to ¾ inch still counts as 1 inch for board feet because you pay for the rough stock.

People also confuse board feet with square feet. A 1-inch-thick board that is 1 square foot in area is exactly 1 board foot. But a 2-inch-thick board of the same area is 2 board feet. Board feet measure volume, not area.

Finally, remember that nominal vs. actual dimensions matter. A 2×4 is actually 1.5 × 3.5 inches, but board foot calculations for rough lumber use the nominal (rough) size. When buying surfaced lumber, use the actual dimensions if you’re comparing to board foot prices.

Choosing the Right Calculator

For most projects, a simple board foot calculator like the one above is enough. But if you’re buying a whole stack of mixed sizes, look for a calculator that lets you add multiple boards and totals them. Some lumber yards provide their own calculators on their websites; those often include the price per board foot and give you a total cost.

When choosing a calculator, check that it accepts thickness in inches and length in feet, since that’s the standard. If you work in metric, you’ll need to convert: 1 board foot = 2,360 cubic centimeters (or 0.00236 cubic meters).

Limits of the Formula

The board foot formula assumes a rectangular board. It doesn’t account for taper, wane, or defects. If you’re buying a log or a slab, the volume is different—use the Doyle or Scribner log rules for logs, not the board foot formula. For irregular shapes, you can approximate by measuring the average width and thickness, but expect some error.

The formula also doesn’t include waste. It gives the nominal volume of the rough board, not the usable volume after cutting. Always add a waste factor based on your project complexity.

Frequently Asked Questions

How many board feet are in a 2x4x8?
A 2×4×8 (nominal 2 inches thick, 4 inches wide, 8 feet long) has (2 × 4 × 8) ÷ 12 = 5.33 board feet. That’s the rough volume; the actual surfaced dimensions are smaller but you pay for the nominal size.

What’s the difference between board foot and linear foot?
A linear foot is just 12 inches of length regardless of width or thickness. A board foot is a volume unit: 1 inch thick × 12 inches wide × 12 inches long. For a 1×12 board, they’re the same, but for any other size they differ.

How do I convert square feet to board feet?
Multiply the square feet by the thickness in inches. For example, 10 square feet of 1-inch-thick wood = 10 board feet. For 2-inch-thick wood, it’s 20 board feet.

Why is lumber sold by board foot instead of by the piece?
Because rough lumber comes in varying widths and thicknesses. Board foot pricing lets you compare the actual wood volume across different sizes. A 6-inch-wide board and an 8-inch-wide board of the same length and thickness contain different amounts of wood, so a per-piece price wouldn’t be fair.

Does the calculator work for metric measurements?
Not directly. Convert to inches and feet first. One inch = 2.54 cm, one foot = 0.3048 m. Or use the cubic centimeter equivalent: 1 board foot = 2,360 cm³.

How much waste should I add?
For simple straight cuts, add 10%. For projects with curves, angles, or grain matching, add 20–30%. It’s better to overestimate; you can always use extra wood for smaller projects.

Related

Formula used
in t | Thickness | in | 1 | 0
in w | Width | in | 6 | 0
in l | Length | ft | 8 | 0
out bdft | Board feet | bd ft | (t * w * l) / 12 | 2
out cost | Cost at $4/bd ft | $ | bdft * 4 | 2

Each line is one input (in, sel, list) or one result (out: label, unit, formula, decimals). How the calculators work

Method: the standard formula for this calculation, rounded as each result states. See how the calculators work or report an error.