Lumber DimensionsFiguring out lumber dimensions can be confusing at first. In fact, the entire first trip to the lumber yard can be intimidating to a new woodworker. However, it is worthwhile getting comfortable going to a place where you can pick and choose the wood you want to work with. The place I go to buy lumber is typical of many lumber yards. It is a large warehouse full of floor to ceiling racks of wood of all different species and sizes.
In most of these types of yards the customer is expected to pick out the wood herself. In order to do this, it is helpful to know about lumber dimensions before you begin.Usually when buying wood you will be using board feet (bf) or linear feet (lf) as the measure of the lumber's dimension. One board foot is one square foot (1” x 12” x 12” or its equivalent). For example a board that is 1” x 6” x 24” is also 1 bf, as is a board that is 2” x 6” x 12”.
A linear foot means that an individual board is sold by length rather than board foot. Wood that has been milled to less than ¾, for instance, is almost always sold by linear foot. To find the price simple multiply the price/lf by the length of the board. For example a piece of 1/2" cherry that is 6" wide might be sold by the linear foot. So a 6 foot board would cost 6 times the price/linear foot. To further confuse things when talking about lumber dimensions, hardwood isn’t referred to by inches, but by quarter inch. A board that is one inch thick is called 4/4 (pronounced “four quarter”) one that is 1 ½” is 6/4 (“six quarter”), 2” is called 8/4 (“eight quarter”), etc. Softwood used for construction purposes, on the other hand, is referred to by inches. For example a 2" x 4" pine board is a "two by four," a 1" x 12 is a "one by twelve," etc. Now that you know the terminology for lumber dimensions you can get down to the actual lumber sizes. You can buy wood that is either rough or finished. The lumber dimension will change depending on which you buy. Rough lumber hasn't been planed or jointed so the boards aren't flat or straight and they are sold in random lengths and widths. Rough lumber is sold at its actual size. In other words, if it says 8/4, the board is two inches thick more or less. Finished lumber, by contrast, has been milled and is sold in nominal sizes. Nominal sizes are the size that the rough lumber ends up after it has been milled. A board that started out at 4/4 will be milled to roughly ¾. However, when figuring out the total board feet for pricing purposes, a board milled to 3/4 will still be considered 4/4, since that is the size of the original (rough) board. In other words, if you have a 3/4" x 12 x 12 piece of wood you still have to pay for a full bf (board foot), not 3/4 of a bf. Lumber dimensions for hardwoods usually has a nominal thickness of ¼” less than the actual. With construction lumber, it is ½” less up to a certain size (2" x 7" wide, I think) where it becomes ¼” smaller. So the familiar 2x4 is actually 1 1/2" x 3 1/2." It does become clear over time, really it does. Take a trip and bring your tape measure. It's fun digging through all that wood! If you like what you read, feel free to sign up for my 'zine Wood Shop News (above the nav bar).
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To calculate a board foot multiply the length of board in inches, by the width of board in inches, by the thickness of board (yes, in inches), then divide by 144 (square inches in a foot). 
