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Board Foot Calculator

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A board foot is 144 cubic inches — a piece one inch thick and a foot square — and it is how hardwood is priced almost everywhere it is sold. The arithmetic is thickness times width times length divided by 144, and the two things that trip people up are both about which dimensions to use: nominal against actual for construction lumber, and hardwood thickness quoted in quarters, where 4/4 means one inch and reading it any other way is wrong by a factor of four.

In whatever currency you buy in

%

For offcuts and defects

4/4 is one inch, 8/4 is two — reading it as anything else is wrong by a factor of four

Softwood, actual sizes:

How to use the board foot calculator

  1. 1Enter the thickness, width and length, choosing the unit beside each — they can differ, which suits the usual mix of inches and feet.
  2. 2For hardwood, use the quarters dropdown: 4/4 is one inch, 8/4 is two.
  3. 3For construction lumber, use the nominal-size buttons, which fill in the actual planed dimensions.
  4. 4Set how many identical pieces you need.
  5. 5Add a waste allowance and a price per board foot to get the figure to actually order and what it will cost.

Examples

A single hardwood board

Input
1 inch × 6 inches × 8 feet
Result
4 board feet

The classic worked example: 1 × 6 × 96 inches is 576 cubic inches, which is four lots of 144.

Thicker stock

Input
8/4 × 8 inches × 10 feet, 3 pieces
Result
40 board feet

8/4 is two inches. Doubling the thickness doubles the board feet, which is why the quarters notation has to be read correctly.

With waste and pricing

Input
4 board feet, 15% waste, £9 per board foot
Result
Buy 4.6 board feet — £41.40

The waste allowance is your estimate, not one this page invents: how much of a board survives depends on its defects and on your cutting list.

About the board foot calculator

Where the 144 comes from

One inch by twelve inches by twelve inches is 144 cubic inches, and that piece is one board foot by definition. So with every dimension expressed in inches, the calculation is simply the product divided by 144. The alternative form — thickness in inches, width in inches, length in feet, divided by 12 — is the same thing with one of the twelves already cancelled, and it is the version most yards use because length is naturally measured in feet.

Because it is a volume, the shape does not matter. Eight board feet is eight board feet whether it arrives as one thick short piece or several thin long ones, and that is exactly what makes it a sensible pricing unit for material that is sold in whatever dimensions the tree allowed.

The unit is essentially North American. Elsewhere, hardwood tends to be sold by the cubic metre for bulk or by the piece for smaller quantities, and the conversion is 1 cubic metre to about 424 board feet. Both figures are given in the results here, since a project sourcing wood from more than one place will meet both.

Buying more than you need, on purpose

The board footage of a cutting list is the volume of wood that ends up in the finished piece. The volume that has to be bought is always larger, and the gap is where a project either stays on budget or does not.

Some of it is unavoidable geometry: parts rarely tile perfectly onto the boards available, so offcuts accumulate at the ends and edges. Some is the material itself — sapwood, knots, checks, cupping and the last few inches of a rough board that are usually split. And some is grain matching, which is the one people forget: if the parts have to look like they came from the same tree, or a panel has to be book-matched, the number of usable boards drops sharply even though the volume has not changed.

The practical habit that follows is to buy the whole quantity at once from the same lot rather than returning for more later. Wood from a different tree, a different kiln batch or a different season will differ in colour and figure, and no amount of accurate board footage compensates for a replacement piece that does not match the rest.

Frequently asked questions

What exactly is a board foot?
A unit of volume equal to 144 cubic inches — the volume of a piece one inch thick, twelve inches wide and twelve inches long. Because it measures volume rather than area or length, a 1×12 and a 2×6 of the same length contain the same number of board feet. That is the point of it: it prices wood by how much material there is, regardless of the proportions it arrives in.
Why is a 2×4 not two inches by four?
Because it was, before it was planed. Construction lumber is sawn to the nominal size, then dried and surfaced on all four sides, which takes it down to about 1½ by 3½ inches. The nominal figure survives as the name and as the basis for pricing, so a 2×4 is sold as a 2×4 while measuring less. Hardwood works differently — it is usually sold rough with the actual dimensions measured, which is why the two need different numbers entering here.
What does 4/4 mean, and why the fractions?
Hardwood thickness is quoted in quarters of an inch, so 4/4 is one inch, 5/4 is an inch and a quarter, and 8/4 is two inches. It is spoken as "four quarter" and "eight quarter". The convention comes from how rough stock is sawn in quarter-inch steps, and it persists because it distinguishes the rough thickness from the finished one — a 4/4 board planed smooth measures about ⅞ of an inch, but it is still bought and priced as 4/4.
How much waste should I allow?
That depends on the wood and on the work, which is why this page takes it as an input rather than inventing a figure. Clear, straight, wide stock cut into small parts might waste 10%. Rough lumber with sapwood, knots and checked ends, cut into long parts that have to be defect-free, can lose 30% or more. The other variable is your cutting list: parts that nest efficiently on a board waste far less than parts that do not.
Is a board foot the same as a linear foot or a square foot?
No, and mixing them up is expensive. A linear foot measures length only, and is how narrow trim and mouldings are usually sold — the cross-section is fixed, so length alone determines the quantity. A square foot measures area, and is how sheet goods and thin stock are sold. A board foot measures volume, which is what matters when thickness varies. A supplier quoting a price will say which, and it is worth checking, because the same number in different units differs by a large multiple.

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