How Much DNA Do Two People Share

How much DNA you share with someone is a critical piece of information in genetic genealogy. The skill of knowing how to use Shared DNA information to predict possible relationships with a match is used often. The amount of Shared DNA is also used to confirm or refute where you or your match fits in a tree – are you in the right place or not.

The first thing to know is the term “Centimorgan”. It is a unit of measure of DNA. Think of a centimorgan like an inch or millimeter.  Each of piece of DNA, or segment, is measured in centimorgans. The DNA companies add up all the different pieces of DNA you share with a match. This total is call your “Shared centimorgans” or Shared cM” or “Shared DNA”. Some companies will even give you the length of the longest segment.  For now, let’s focus on the total amount of shared DNA.

To learn more about the tools that estimate relationships, please go to the Tools Category