If you’re puzzled over the expression “second cousin once removed” or “twice removed,” you’re not alone. Luckily, the answer is simple: All cousins share a common ancestor. Your “degree of cousinhood” (second, third, fourth) depends on how many generations back that common ancestor is. Knowing this, you can make your own cousin calculator.
Take your first cousins, who you know are your aunts’ and uncles’ children. You all have the same grandparents. Your second cousins share a set of great-grandparents with you, your third cousins have the same great-great grandparents, and so forth. So your granddaughter and your sister’s grandson would be second cousins, for example—they have two generations between them and the common ancestor (your parents).
“Removes” enter the picture when two relatives don’t have the same number of generations between them and their most recent common ancestor. One generation difference equals one remove.
Let’s go back to the previous example—say your granddaughter has a son. He has three generations between him and the common ancestor (your parents), but your sister’s grandson still has only two generations in-between.
So they would be second cousins, but once removed. Likewise, your grandparents’ cousins are your first cousins twice removed because of the two-generation difference from you to your grandparents. Your great-great-grandparents are still the common ancestor.
Recent Common Ancestor
First identify the most recent common ancestor for the two relatives in question. Then find each relative’s relationship to that ancestor on the sides of the chart. Where the row and column meet, you’ll find their relationship.
You can read more about relationships in Kinship: It’s All Relative, 2nd edition, by Jackie Smith Arnold (Genealogical Publishing Co.).