Log purchasers use many reasons for the differences in log rules. For example, users of the Doyle Rule, which underestimates volume in smaller logs, say that this is the very reason it is a fairer rule in that it costs them more to process smaller logs. This is logical since the logger will have to cut more trees, the sawyer will have to saw more logs, and the yard crew will have to move more logs to the sawyer, to equal the amount of lumber in much larger logs. However, if he cannot efficiently utilize smaller logs, he should base his offer on that, not on a biased estimation of yield. There are other reasons given to justify variance in log rule use, but frankly, none hold much water for me. As we can see, there is the potential for dishonesty when choosing log rules.
From the time the very first Europeans set foot on American soil, we have tried to develop systems to estimate the board feet of finished lumber we can obtain from a green log. It seems straightforward: figure the number of 1-inch thick planks that can be sawn, subtract for the width of the saw blade (kerf) and for waste (trim), and there you would have it, what is known as a “log rule.” However, it is not that simple, because that does not take into consideration the high variability between logs, equipment used to saw those logs, and the operators of that equipment. The Forest Service’s Forest Products Lab in Madison, Wisconsin reports that over 95 log rules with about 185 different names have been developed in our brief history as a nation.
Foresters use a number of mathematical formulas to estimate the board feet of lumber in a cut log. Using one of these formulas, known as “log rules,” you, too, can estimate the amount of sawn lumber a log will produce. This can be useful, say, if you may want to estimate what you will owe the portable sawmill owner for sawing it up for you (since he probably will charge you per board foot). The estimate will get you close so that the final bill will not be a complete surprise.