The DNA relationship statistics listed at ISOGG are invaluable for figuring out how you are related to new DNA relatives. This diagram shown there is a big help too:
DNA relatedness cousin tree courtesy Dimario, Wikimedia Commons
More statistics would be even better so I am delighted to make the following request.
Genetic genealogicist Blaine Bettinger has decided to collect cM numbers for known close relationships from all of us who have tested. Read about it on his blog and then contribute yours. He wants family statistics out to 3rd cousins.
Blaine explains how easy to provide those numbers if you are tested at Family Tree DNA, but 23andme includes the X in their totals which skews the results. Plus they include segments smaller than 7cM which is not what Blaine wants. So I decided to make a step-by-step how-to for 23andme statistics collection.
Better is if your 23andme or Ancestry.com tested family members are all uploaded to GEDmatch.com. Then you can easily get the statistics there. Just run the one-to-many with the normal default of 7cM for each family kit and look in the columns Total cM and largest cM under Autosomal.