Dear Eric, There are some probabilities here, but my suggestion is that you only use a "formula" for people who share more than about 75 cMs with you. Such people are likely to be 3rd cousins or closer. For people who share about 50 cM to 75 cMs, the probabilities favor 3rd cousins once removed to 2nd cousins once removed. Below 50 cMs, I categorize them all as "distant" cousins to 3rd cousins until I can better sort out the exact relationship using either genetic analysis or from genealogical research. I use cousin clusters and run comparisons to determine how much DNA a new match shares on average with the appropriate cousin cluster. This allows me to be more precise in terms of predicting the true genealogical relationship than I can be if I only do a one-to-one comparison. Sincerely, Tim Janzen -----Original Message----- From: GENEALOGY-DNA [mailto:[email protected]] On Behalf Of Eric S Johnson Sent: Saturday, August 26, 2017 12:06 AM To: [email protected] Subject: [DNA] cM v. segments Does anyone have any idea what kind of a formula could be used to compare the "likely closeness of the relationship (on average)" of two "DNA cousins" who share a number of segments? 23andMe, for instance, ranks more highly someone who shares 40 cM in 3 HIRs than someone else who shares 45 cM in 2 HIRs. Best, Eric