A board foot (bd. ft.) is the unit of measurement for hardwood lumber 1" or thicker
To calculate, measure the board Length x Width x Thickness (IN INCHES!) and divide by 144.
Example:
A board that is 8' long x 6" wide x 2" thick.
96 x 6 x 2 = 1152 / 144 = 8 board feet.
Now multiply 8 x the price per board foot to get your total.
What's with all the weird fractions? (4/4, 5/4, 6/4, 8/4, etc.)
All rough lumber thicknesses are measured by the ¼ of inch. The first number is how many ¼ inches there are.
Common Sizes: 4/4 = 1” 5/4 = 1-1/4” 6/4 = 1-1/2” 8/4 = 2” 10/4 = 2-1/2” 12/4 = 3” 16/4 = 4”
While you might be used to seeing sizes like 1×6 or 2×8 in lumberyards for softwoods (fir, pine, cedar, etc.) Softwoods that get sold in “standard” sizes like 1×6 and 2×8 are cut for particular applications that require those sizes. In building construction you’ll find standard and uniform sizes from building to building. Door jambs and wall studs for example.
The hardwood industry takes a different approach.
That’s because the primary users of hardwoods (red oak, cherry, maple, walnut, etc.) build custom or made-to-fit products – like furniture and cabinetry – where uniform sizes in the raw material is unnecessary and more troublesome. For example, there’s no standard size for kitchen tables, you can make one any size you want. So sawmills cut hardwood logs to get the best yield from a log, which means all boards will be various in width rather than the same width.
If sawmills were to cut logs to specific sizes or uniform widths, that process would incur more waste and require more labor. Therefore the resulting boards would cost you more money. Who wants that?
So, the hardwood industry standard for indicating the size starts with lumber thickness, and it’s expressed as a fraction: 4/4, 5/4, 6/4, 8/4 and so on.
This system of naming lumber thickness by quarters was established by the National Hardwood Lumber Association. The organization was founded in 1898 to establish a uniform system of grading rules for the measurement and inspection of hardwood lumber.
A saw that cuts lumber from a log is very large and aggressive, so the resulting lumber is known as “rough sawn” and the surfaces of the boards are . . . yes, rough and inconsistent. This lumber needs to be planed smooth and flat before being sized for the project at hand. When lumber is bundled together, it is usually done by thickness and length. The widths of the boards are usually random as the sawmill is trying to get the most yield from the log.
ALL of our lumber is rough sawn. Some of our wood may look as though its been planed and jointed, and it may have been, at one time. However, wood is a product of nature and has internal stresses that exert pressure on the board as time passes.
Any board that has been machined to size, and then left to sit will most likely deform a little over time. Therefor it is important to use the wood soon after you have machined it to is final size. Do not S4S your wood all at once thinking that you will same yourself time later. Only square up what you need WHEN you need it.
The 1/4" scale used in rough lumber is ...... you guessed it ....... ROUGH! Board thickness will vary slightly over the length of the board. Since rough lumber is intended to be machined down to a specific size, you will need to buy wood that is thicker than the final dimension of your project.
When planning a project, most people tend to think and layout things in their final, or finished, dimensions. Always remember to account for the fact that you have to cut and finish the wood to it final size.
For Example: Your plan is to make a table top that has finished thickness of 1". If you were to buy 4/4 (1") thick rough lumber, once you plane and joint the wood to make it S4S (square on all four sides), your boards will be less than 1" thick.
Board footage helps you make an educated guess as to how much lumber you'll need. Afterall, you'll be cutting and/or gluing your project parts from boards of various sizes.
Always plan to buy extra to make sure you're covered. You will need to cut out your parts, glue up to width, arrange grain patterns and color, fix mistakes, make test cuts on joinery set-ups, and test finishes. All parts of your project that use up wood. If you're new to wood working, I would strongly suggest buying 20% more than you thin you'll need as you WILL make mistakes. As you improve and hone your skills, you will be able to lower that number.