Board Feet: What is it?

When we look at lumber, we have a number of ways to see it: rough cut, dimensional and board feet.  The questions in this are: Why isn’t a 2X4 actually 2” X 4”? And why is Board Feet used in pricing?  For me, knowing this is one thing but understanding it is altogether different.

We generally recognize the 2X4, 2X6, 4X4, 1X2 and all the rest.  These measurements refer to the thickness and width of the lumber. We also know that these are not the finished measurement of the lumber thickness or width. The true size of a 2X4 is about 1.5″ X 3.5″.  When the board is first sawn, however, it is a true 2X4.  The drying and planing of the board reduce it to the finished 1.5″ X 3.5″ size. The lumber is then sold as a “2X4” – which is the cost of the wood before being removed during the drying, planing and processing that must be paid for. It is also easier to refer to a board as a 2X4 than as a 1.5 X 3.5.

So a tree is cut into pieces (called cants), the green wood is air dried, cut up into boards, and then dried again. Some lumber is “kiln dried” in order to speed up the process and gain a little more control over the moisture content (which has the side benefit of killing any bugs living inside).  One of my favorite words is “hygroscopic” – which is a material (like wood) that tends to absorb water. The drying process helps to control this process and is key to helping control future problems with warpage.  Once dried, the lumber is planed to its dimensional size.

This is where Board Feet come in handy. In general, Board Feet is used for pricing and it sets the measurement for the basic cost of wood. Most of us at the Estimating/Construction end brush up against board feet, but we don’t have a lot of use for it – if you order 1000 2X4X8 boards you know exactly what you have to build your project.  For the same cost you could just order 5,333.333 BF, but that could also be fulfilled with 134 pieces of 6X8X10 – not quite what you wanted!  Basically, Board Feet allows the Lumber Industry to set their prices for the volume of wood and this allows pricing to be even across the board.

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