How to calculate board feet

1. What a board foot actually is

A board foot is a unit of volume, not length or area, and it is the standard way North American lumber yards measure and price solid wood. By definition one board foot equals 144 cubic inches. The easiest mental picture is a piece of wood one foot wide, one foot long and one inch thick — that single piece is one board foot. Because it is a fixed volume, the shape does not matter: a 1×12 that is a foot long, a 2×6 that is a foot long and a 4×3 that is a foot long all contain exactly one board foot of wood. That is the whole point of the unit — it lets a yard price a thick, narrow plank and a thin, wide one on the same scale, by how much actual timber each contains.

This is also why board feet matter more for some purchases than others. Trim and moulding are usually sold by the linear foot because their cross-section is fixed, and sheet goods such as plywood are sold by the square foot because their thickness is fixed. Rough lumber, hardwood and bulk framing stock vary in all three dimensions, so they are sold by the board foot, the one unit that captures the full volume of wood you are paying for.

2. The formula, two ways

There are two equivalent forms of the board-foot formula, and which one is easier depends on whether your length is in feet or inches:

• Length in feet:board feet = thickness(in) × width(in) × length(ft) ÷ 12. The 12 appears because there are 12 inches in the "length" foot you have not yet converted.
• Length in inches: board feet = thickness(in) × width(in) × length(in) ÷ 144. Here you divide by 144 because that is the number of cubic inches in one board foot.

Take a 2×6 that is 12 feet long. Using the first form: 2 × 6 × 12 ÷ 12 = 12 board feet. Using the second, with the length converted to 144 inches: 2 × 6 × 144 ÷ 144 = 12 board feet. Same answer, as it must be. For a whole order you calculate one board, then multiply by the quantity: a stack of 25 of those 2×6×12s is 25 × 12 = 300 board feet. The calculator does both steps and the unit conversion in one shot, including a metric mode that reads millimetres and metres and still reports board feet.

3. Board feet chart for common lumber

Board feet per piece for standard nominal dimensional lumber at common lengths. Multiply the value by how many boards you are buying.

These figures use the nominal sizes, which is how dimensional lumber is conventionally tallied (see the next section). They are also a quick way to cost a framing package: total the board feet across all the sizes on your cut list, then multiply by the yard's price per board foot — or per MBF, the thousand-board-foot unit bulk timber is often quoted in.

4. Nominal vs actual size — the trap

The single thing that confuses people most about board feet is which dimensions to use. A 2×4 does not actually measure 2 inches by 4 inches — it is dressed, planed and dried down to about 1½ by 3½ inches. So should you tally it as 2×4 or as 1½ × 3½? The well-established convention is that softwood dimensional lumber is tallied from its nominal size: a 2×4 counts as 2 × 4 even though it is smaller, because that is how the trade has always priced and sold it. That is why the chart above uses nominal figures.

Rough-sawn hardwood is the opposite. It is measured from its actualsawn dimensions, and its thickness is quoted in quarters of an inch: 4/4 ("four-quarter") is a board roughly 1 inch thick, 5/4 is about 1¼ inch, and 8/4 is about 2 inches. A hardwood dealer who quotes you 4/4 walnut at a price per board foot is measuring the actual rough board, width to the nearest inch and thickness in quarters. The practical rule: enter the numbers that match how the wood is described and sold to you — nominal for construction lumber, actual for hardwood — and the board-foot tally will line up with the invoice.

5. Estimating board feet from a log

If you are milling your own lumber, the question flips: how many board feet of usable lumber can you expect to saw out of a log? You cannot simply use the log's volume, because the saw kerf, the slabs and the taper all become waste. Foresters and sawyers use log rules for this — the three common ones in North America are the Doyle, the Scribner and the International ¼-inch rules. Each takes the small-end diameter and the length of the log and estimates the board-foot yield, and they deliberately give different answers: the Doyle rule underestimates small logs, the International ¼-inch rule is the most accurate, and Scribner sits between them.

The takeaway is that a log rule is an estimate of finished yield, while the board-foot formula on this page measures wood you have already cut to known dimensions. For planning a build, lay out your cut list of finished boards, board-foot each line with the calculator, and add a sensible waste margin for defects, snipe and trimming. If your project also involves framing or sheet goods, the stair calculator and the other tools on the carpentry hub handle the layout side while this one handles the timber tally.

Common questions

What is the formula for board feet?

Board feet = thickness (inches) × width (inches) × length (feet) ÷ 12. If you keep the length in inches instead, divide by 144. Both work because one board foot is defined as 144 cubic inches of wood.

How many board feet are in a 2×4×8?

5.33 board feet: 2 × 4 × 8 ÷ 12 = 5.33. Use the nominal 2 and 4, not the dressed 1½ × 3½, when tallying dimensional lumber.

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

A square foot measures area (width × length) and ignores thickness; a board foot measures volume and includes thickness. Sheet goods like plywood are sold by the square foot, while solid lumber is sold by the board foot.

What does MBF mean in lumber pricing?

MBF means one thousand board feet (the M is the Roman numeral for 1,000). Bulk lumber and timber are often quoted per MBF, so a price of $600/MBF is 60 cents per board foot.