Lumber measurement

Demystifying the rules and scales for measuring lumber. July 24, 2001

Question
I am confused about BF, cf, and all the different measures. I read that a log 16" in diameter and 8' long will produce 85 BF, but plugging it into the Int formula I get 81 BF. Also the Doyle, Int and Scribner formulas produce different results. What is a 4/4 piece--is it 4" x 4" or 1" thick? What is 5/4 and 6/4?

Forum Responses
Indeed, log rules and lumber measurement are different. Also, when calculating log volumes, many rules go to the closest 10 BF.

Different rules give different results. Int 1/4-inch rule gives the closest estimate for yield for a circular mill. There is also an Int 1/8 rule that would be closer for a band mill. Scribner and Doyle underestimate the volume with smaller log sizes. The reason is that a smaller log takes more handling, so you could either measure accurately and then pay less for a smaller log due to increased handling, or just pay the same price for all volumes, but underestimate the volume for those smaller logs.

4/4 lumber (pronounced "four quarter" and meaning four 1/4-inches thickness, and four 1/4-inches totals 1 inch) is lumber that is 1.00" to 1.24" thick. This thickness is measured at the thinnest spot used to establish the grade of the piece, for hardwoods. For softwoods, 4/4 is seldom used for green lumber, but is used mainly for lumber after is planed, in which case, 4/4 means 0.75" thick at the time of planing.

5/4 would be five 1/4" or a minimum of 1.25" for hardwoods, etc. 6/4 is 1-1/2" minimum, etc.

Gene Wengert, forum technical advisor


Keep in mind the purpose for which the measuring is done. If you're cutting logs, the reason for measure is the next person using it. This is why, I think, log measures are larger, i.e. gross amounts (for milling), milling measures slightly finer (accounting for surfacing), log cuts as amounts (board feet of boards), going again to finer, more net amounts, (4/4, 8/4), (s1s, s2s 1e,) for end use (furniture and cabinetmakers). Most lumber never even gets sold into these finer grades. The only measures needed are those for the next user and the price at that stage. The actual measures always reflect what is direct, simple, and quickly establishes price.

The sawmill language is really very simple. One of the reasons for using the quarter method for thickness came from the sawyers. They had to tell the block setters on the carriage what thickness to set to make a cut. The sawyer would hold up 4 fingers, the block setter would set on 1.5 fingers = 5/4, 1 finger = 6/4, 2 = 7/4, 3 = 8/4. For cutting timbers the sawyer would point his hand down 4 fingers = 4", 1 finger 6", 3 fingers = 8", 5 fingers =10", fist = 12".

As for lumber sticks, I have seen it from a logging and sawmill standpoint. We use the Doyle scale. On small logs the scale goes in favor of the sawmill, but you cut less high-grade lumber from small logs. The overrun makes up for the loss in grade. On large logs the logger gets the overrun. If the logger brings nice big logs, everybody wins. Sawmills can't stay in business cutting small low-grade logs. High-grade logs will yield high-grade lumber. Sawmills usually set their #2 price of lumber at their log cost. This leaves them a profit on their upper grades only.