The Sawtimber Measurement
A round log, generally, must be made into square or rectangular pieces to be able to determine wood volume and value. Three systems, or log rules and scales, have been developed to do just this. They are called the Doyle rule, Scribner rule, and International rule . They were developed to estimate board foot mill tally, usually quoted as thousand board feet or MBF.
Our problem when using these log rules or scales is that they will give you three different volumes for the same pile of logs. Measuring average sized logs - Doyle, Scribner, and International rules - will give volumes that may vary as much as 50%. This "overrun" is greatest using Doyle and the least using International. Buyers like to purchase using Doyle log rule while sellers like to sell using Scribner or International.
There will always be a difference in volumes estimated from scaler to scaler. They get into trouble when decreasing actual number of measurements and start estimating; they measure at inappropriate points on the log, miss estimate roundness, and don't deduct for defect. Accurate scaling of trees and logs requires skill and experience.
The Conversion Factor
Mensurationists cringe at the word conversion factor. They correctly feel that conversion from one unit of measure to another unit of measure of wood is too imprecise to depend on. Their job is to be precise.
But you have to have some way to estimate volumes and be able to cross over to differing units. You now have an idea of how complicated this volume issue can become. To add a conversion factor to volumes may distort actual volumes even more.
With this warning I offer you a list of approximate conversions at the Approximate Conversions of the Most Common Units of Wood Measure site.