For the program to consider two people a potential match, the largest matching DNA segment between two people must be at least 5.5 centiMorgans (cM) long.* The program then uses additional matching segments to confirm the relationship and to calculate the degree of relatedness.

Based on the extensive Family Finder database, it is rare for two genuine genealogical cousins to have a largest shared segment of less than 7 cM and one less than 6 cM is exceptional.

*updated from 5 cM 15 Aug. 2012