Try looking at the following... thread507-126960
They aren't really compatible methods but a while back I tried to work out an equivalent. Note that most comments in the thread did not support what I was trying to do. What I wanted was to develop a rule-of-thumb as a general guideline. It required that you make several assumptions and go partially through the calculations.
The assumptions made regarding site class and the value of R which impact the final answer greatly. Also you need to be careful with strength versus allowable stress which is a factor of 1.4
Regards,
-Mike