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.