Question
I am in Portland, Oregon and I need to know the estimated height of a Douglas Fir tree considering medium growth rate and not knowing the DBH because the tree has been cut down and removed.  The remaining trunk is 4 inches high, and has a diameter of 7 1/2 inches.  Also, is there a regression test that can determine this?

Answer
Here is one web link to information as it relates to DBH diameters and height showing a 7 inch Doug fir has a height of around 50-55 feet tall. Figure 2 in the attached research.

http://ir.library.oregonstate.edu/jspui/bitstream/1957/7739/1/RC25.pdf

I would contact the Oregon State Forestry agency and ask one of their Foresters to help. Sounds like more to the question than just the height. Thy maybe able to assist or give you the name of a Consultant Forester who can assist in an on the ground measurement or in a court case if needed.

Here is their contact information,  http://www.oregon.gov/ODF/contact_us.shtml