|If one person's →||Grandparent||Great-grandparent||Great-great-grandparent||Great-Great-Great-grandparent||Great-Great-Great-Great-grandparent||Great-Great-Great-Great-Great-grandparent|
|is the other person's
|then they are|
|Grandparent||1st cousins||1st cousins once removed||1st cousins twice removed||1st cousins thrice removed||1st cousins four times removed||1st cousins five times removed|
|Great-grandparent||1st cousins once removed||2nd cousins||2nd cousins once removed||2nd cousins twice removed||2nd cousins thrice removed||2nd cousins four times removed|
|Great-great-grandparent||1st cousins twice removed||2nd cousins once removed||3rd cousins||3rd cousins once removed||3rd cousins twice removed||3rd cousins thrice removed|
|Great-Great-Great-grandparent||1st cousins thrice removed||2nd cousins twice removed||3rd cousins once removed||4th cousins||4th cousins once removed||4th cousins twice removed|
|Great-Great-Great-Great-grandparent||1st cousins four times removed||2nd cousins thrice removed||3rd cousins twice removed||4th cousins once removed||5th cousins||5th cousins once removed|
|Great-Great-Great-Great-Great-grandparent||1st cousins five times removed||2nd cousins four times removed||3rd cousins thrice removed||4th cousins twice removed||5th cousins once removed||6th cousins|
There is a mathematical way to identify the degree of cousinship shared by two individuals. Each "great" or "grand" in the description of one individual's relationship to the common ancestor has a numerical value of 1. For example, if person one's great-great-great grandfather is person two's grandfather, then person one's "number" is 4 (great + great + great + grand = 4) and if person two's "number" is 1 (grand = 1). The smaller of the two numbers is the degree of cousinship. The two people in this example are first cousins. The difference between the two people's "numbers" is the degree of removal. In this case, the two people are thrice (4 - 1 = 3) removed, making them first cousins thrice removed
Example 2: If someone's great-great-great grandparent (great + great + great + grand = 4) is another person's great-great-great grandparent (great + great + great + grand = 4), then the two people are 4th cousins. There is no degree of removal, because they are on the same generational level (4 - 4 = 0).
Example 3: If one person's great grandparent (great + grand = 2) is a second person's great-great-great-great-great grandparent (great + great + great + great + great + grand = 6), then the two are second cousins four times removed. The first person's "number" (2) is the lowest, making them second cousins. The difference between the two numbers is 4 (6 - 2 = 4), which is the degree of removal (generational difference) ...
The removal (once removed, twice removed, etc.) indicates the number of generations, if any, separating the two cousins from each other. The child of one's first cousin is one's first cousin once removed because the one generation separation represents one removal. Oneself and the child are still considered first cousins, as one's grandparent (this child's great-grandparent), as the most recent common ancestor, represents one degree ...