Calculating board footage

Professor Gene Wengert explains it all. February 18, 2003

How do you calculate board footage? Do you calculate board footage using 4/4, 5/4, 6/4, and so on for thickness dimensions? Or do you use the actual width (for example, 4/4 is actually 1 1/8 inches thick)? The Wood-Mizer scale that was posted here just multiplies width x thickness x length (in inches) divided by 144; however, from the reading I have done, that is not how it is calculated. A lot of customers rely on 144 cubic inches = 1 board foot.

Forum Responses
From WOODWEB's Sawing and Drying Forum
There is only one way to measure the footage of hardwood *lumber* (and another for softwood). This technique is subscribed to by all the Departments of Commerce in all the states. It is simple. Any variations are a violation of state's weights and measures laws.

For hardwoods: First, you need to use the standard length (4', 5', 6', etc. and not include any inches over the standard length). However, 12'11" is still 12'. Then multiply by the actual width in inches and fractions and then divide by 12. Now round to the closest whole number. This is called the surface measure (SM). If you have several pieces of the same thickness, add up all their SMs. Finally, multiply by the *standard* thickness in inches (not actual). So, a piece 1-7/32" thick is 4/4, so the multiplier is 1. Apices 1-15/32 is 5/4, so use 1.25. The final answer is a whole number and not fractions.

For softwoods, you would use the standard width (not actual). You would also use two decimal places for SM and BF. Otherwise, it is the same as for hardwoods.

Did the scale that was posted calculate for lumber or for *logs*?

Most mills do not calculate board footage, but use a small stick of wood that has the footage numbers already on it (silk-screened). The stick is called a lumber rule. The calculations above for hardwoods and the stick agree 100%. You can also get this rule in a "steel-tape" version.

Gene Wengert, forum technical advisor

From contributor C:

Gene, if I read you right, a board 1x8x8' has 5 1/3 actual feet but can only be called 5 feet. Therefore a stack of 100 1x8x8 has only 500 feet rather than 533. To be fair to myself my pricing must take this into account rather than charging for 533 feet.

For softwoods, you would use 5.33 BF. For hardwoods, 5 BF. For softwoods, the actual size would be 7.25" wide, but we base footage on the nominal size, not actual for softwoods. For hardwoods, we would use 7.25" or whatever the actual width is.

However, hardwood lumber would not be usually manufactured to exactly 8.0" wide, but would be random width. So, half of the pieces would be under 5.000 BF and half would be over. If you are making something like finished lumber and selling it by the piece, certainly you can adjust the price per piece as needed.

Note that a 1 x 7.00" x 8' has 5 BF (or using decimals, 4.67 BF per piece). Are you planning to sell this at a lower cost?

Gene Wengert, forum technical advisor

From contributor C:
We sell just ERC. Most of our customers are buying for projects, wall covering, etc and need a certain number of square feet. Many are very specific on width and thickness. So we calculate actual square footage and charge for this. We very seldom saw a random width. We make cants to a specified size and resaw. When selling 4/4 to lumber yards and furniture manufactures, it is usually graded and measured at the user end.

With a valuable wood, it is reasonable to sell by the square footage (including fractions) and not the board footage.

(Note: For wood under 1.00" thick, when measuring BF, you always use 1.00 for thickness. This means that when a piece that is 1-1/8" thick is resawn into two pieces, each about 1/2 inch thick, you will double the board footage!)

Gene Wengert, forum technical advisor

Fellows, you have me all confused. What am I doing wrong? I thought a1x6x12 would be 6 BF.

It is. And so is a 1/2 x 6 x 12.

And if this is a 1 x 6 x 12 softwood, then the actual size could be 3/4" x 5.5" x 12' and still it is 6 BF.

Gene Wengert, forum technical advisor

Gene, I agree with your comment "However, 12'11" is still 12'" for standard grades. In the case of something like mahogany it would be 13' unless this has changed since the 1986 rule book. I have started many an argument by saying I could have 2 boards both with the same dimensions with different board foot measurements (different species).