This is part of what Neches (http://neches.bp-3cloud.com) does when it analyzes the overall complexity of your solution. It calculates this score for both BPDs and Services. The right way to do this IMO, is based off of graph theory using control flow complexity to calculate the answer. You can read more about how to do this here - http://eden.dei.uc.pt/~jcardoso/Research/Papers/JA-2008-017-JWSR-Business-Process-Control-Flow-Complexity-proof.pdf
Note that this represents only 2 of over 20 rules Neches uses to attempt to assess the overall complexity of your solution.