Board-Foot Lumber Measurement Confusion

A woodworker tries to figure out how to make sure he's ordering and getting the amount of wood he actually needs. January 20, 2010

The max allowable shrinkage and waste when buying kiln dried and straight lined one edge, some lumber sheds sell me 500bf and I get 500bf and then some seem to short me. Last time I balked they told me this and that about shrinkage and dimensioning. What is the allowable standard? I love getting over the footage I pay for, but do understand that a 2x4 is not 2"x4". Whatís the excepted allowance?

Forum Responses
(Cabinetmaking Forum)
From contributor L:
The lumber trade used to deduct a kiln shrinkage amount, 7%+-, but that's not allowed anymore. You should be getting net tally. They will tally the lumber before further processing (straight line etc.) So you will pay for but not get whatever is lost in the SL process. Lots of places use a method of calculating bd ft that I find unacceptable. They stack the lumber and measure across the width of the stack and use that in their calculation. So the space between crooked boards becomes "air lumber". When they piece tally they use the closest inch for width. So if the mill has managed to cut 5 9/16" boards they count as 6" wide (about 7% their gain, your loss). In theory it averages out. When it is someone elseís wood you are straight lining. You make sure you take off enough to not have problems with narrow strips jambing in the feed chain.

From the original questioner:
When I count bf per piece I measure width in the middle of board since one end is wider than the other even though I know it not the usable width, I figured it was splitting the difference. It was 11.5% less than I paid for, but at $1.38 a bf for red oak FAS 13/16 KDSL1E then factor in the shortage it comes to $1.54 BF. Is that in line with the rest of you guys? I actually know some guys asking that for rough sawn, but donít know if it's a great deal or no deal at all.

From contributor S:
If block scale is not acceptable because "air lumber" and measuring to the closest inch is no good for you , what method will work? If there is wood that is over eight feet that is usable shouldn't you pay for that? If you get over scale do you say anything? If you guys are having these issues I would find a different source for wood.

From Carl Hagstrom, Systems Administrator at WOODWEB
You may want to read the Knowledge Base article below. It was written in '01, but as far as I know, the content still applies now. My understanding is that there are well defined rules governing this issue. If we're lucky, Prof Gene Wengert may weigh in as well. From everything I've read about this topic, true measures are not based on opinion, but on a well defined and prescriptive method.

Gross Vs Net Measure

From the original questioner:
Measuring to the closest inch is fine by me, as long as we all do the same thing. I will round up and add an inch just to give them the benefit of the doubt. What I was looking for was this part - "true measures are not based on opinion, but on a well defined and prescriptive method".

I just need that method so I can have all suppliers on the same page, because when I order 87BF to do a job thatís what I need to do the job not 12% less to allow for shrinkage and straight lining. You see 1 S4S bf is 11 1/4'' wide but 12'' long. I think we can use the link provided by Carl and get through this.

From Gene Wengert, forum technical advisor:
The measurement of lumber is strictly controlled. Softwood lumber is measured differently than hardwood. The allowable shrinkage is zero for hardwoods. However, for softwoods, the actual size is based on the MC and the size at the time of grading. If the MC is higher than the level that you are using and the wood has dried, it will be smaller. However, for softwoods, the BF will not have changed with this shrinkage, even if the shrinkage occurred before you bought the lumber.

For hardwoods, if you purchase 500 BF, you should and must receive that amount (within a few BF). Block tally techniques can be used, but air space cannot be included. In fact, if a piece of hardwood is warped edgewise (called side bend), it is almost 100% that the grade has dropped, as the clear areas used for grading cannot be curved or in different angles.

For tapered lumber, the width is measured 1/3 from the narrowest end, not in the middle. Now, here is where we have some problems. If lumber is remanufactured, such as straight-line ripped, then the footage can be based on the footage of the lumber used to achieve the manufactured lumber and not the footage of the SLR pieces. In fact, SLR pieces may be measured in a different way, such as using the total square inches and then dividing by 12 and then using fractions as well (such as 3.2 BF or 3-1/4 BF). In other words, the grading rules and the measurement used for lumber often is not appropriate for remanufactured pieces. However, you can eliminate the confusion by specifying what it is you want to buy..."535 BF measured after SLR."

Additional info: you probably should specify species (red oak or hard maple is not enough if you want specific color-indicate color too), thickness (4/4 is not enough; specify 25/32" hit and miss), moisture content (KD is not enough; use an actual value such as 7.0% MC with nothing under 6.0% MC and over 8.0% MC measured with a xxx brand moisture meter) and footage of the pieces after SLR.