The numbers are basically what I have seen over the past 15+ years of sawing wood. I would stand by these numbers. Once over a certain size/age tree, say White pine, the 2" sap ring will always be this size, yielding more heart wood as the tree grows. So, percentages would not be the solution. Just subtract 2" off the size of the tree, for White pine. Cedar, I would almost kill for a 20" log. Red Pine just simply has a lot of sap wood, a 12" log could easily have a 2" heart and 10" of sap. I don't know how souther pine stands up to Red pine in similarity, I bet it is close.
Tim
