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CALCULATING BOARD FEET, page 3
As discussed on page one of this document, "Board Feet" is the standard unit of measurement used in calculating the volume of rough lumber that is bought and sold in the hardwood and softwood lumber trading industry.
The basic concept of how to calculate board feet is relatively simple, but in reality there are always a few concepts that confuse the casual user.. like the shrinking wood aspect discussed in the previous article.
I'll go through the math and maybe a few examples, but the key piece of information to grasp is that a board foot can come in many forms, varying in width, thickness or length as long as the unit of volume stays the same.
One Board foot always equals 144 cubic inches
Width (in inches)
x Length ( in inches)
x Thickness (in inches)
/ divided by 144
(144 cu inches per board foot-this converts length/width to feet)= # of board feet
Example #1: how to calculate board feet?
For example for a piece of wood 6" wide x 24" long by 1" thick , we take the width measured in inches and multiple it by the length (in inches) and multiple this by the thickness in inches. Then divide that by 144 and you'll have succeeded in calculating board feet.
6" wide by 24 " long by 1 " thick/144 = (6*24*1)/144 = 144/144 = 1BF
Now if the same board was 2" thick the calculation would be almost the same.
6" wide by 24 " long by 2" thick/144 = (6x 24x 2)/144 = 2 BF
OK I know you're saying enough, enough..
So what is the trick to calculating board feet:
Example #2
It is mostly about keeping the units of measurement straight. Use this variant of the equation if you are measuring the length in feet:
Width (in inches) / divided by 12 (to convert to feet)
x Length ( in feet, or converted from inches)
x Thickness (in inches)
= board feet
Thus something 6" wide, 10' long and 2" thick would be (6"/12)*10'*2"= 10 bf
Something: 6" wide, 10' long and 1 1/4" thick would be (6"/12)*10'*1.25 = 6.25bf
The actual process of calculating board feet is not complex but for some reason the number 12 keeps getting in the way. Find one approach that works for you and then every time you need to know the math use the same process.
If everything is in inches and then you divide it all by 144 at the end, that works. if you prefer to keep the width and thickness in inches and the length in feet, then divide the result by 12, that works too.
One last note..
Since the big boys have no interest in adding up an entire list of fractional widths of lumber when calculating board feet, they have invented a special scaling ruler that can be laid on a board and instantly show you how much wood is in that plank without having to have a calculator handy to do the math.
This averages the width of every board to round off the amount of wood in each board to a single number, like 5 or 7BF. So for instance a piece of wood anywhere between 5.5" and 6.5" in width would be treated as if they were 6" wide. Sometimes you win with all the boards over the 6" and sometimes you lose and all the boards are 5.5", so the math is not quite as precise as I might lead you to believe.
If you are interest in seeing how they use a scaling ruler sign up for our free woodworking class online that shows you how to calculate board feet and the basics of lumber grading so that you can figure out what you need for a project and know that you are getting the right quantity and grade to fit your needs. Board Foot Calculator available from the class notes section of this page.
Our next article in this series discusses converting square footage to board feet, probably much easier math than doing the initial board foot calculation.
More Information
Learn More About How to Buy Wood or Lumber Online: buying, drying and choosing? What are lumber grades? and more...
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