A relationship between two persons can be determined if a common ancestor (e.g. parents, grandparents, etc.) is known. To determine the relationship, first put the name of the common ancestor (i.e. one whom the two persons are directly descended from) into the box at the top left of the table below.
Then, going to the right of the common ancestor, put one of the two persons into the appropriate generation that he/she is from the common ancestor (eg. if the person is a great great grandchild to the common ancestor, then the person is in the fourth generation from the common ancestor, thus the person goes into the Gen4 box that's labeled 2G GChild).
Next, going down from the common ancestor, put the other of the two persons into the appropriate generation that he/she is from the common ancestor (in the same manner as did for the first person).
Last, follow down the generation of the first person and follow right the generation of the second person to the intersecting box. The label in that intersecting box shows how the two persons are related.
Example: To you and Jane Doe the first common ancestor is John Smith. To you, he is your great grandfather. So your name goes into “Gen3” in the left margin. To Jane, John is her grandfather. So her name goes into “Gen2” across the top. Your row and Jane’s column intersect at “1C 1R”. Thus, you and Jane are “first cousins once removed”.
The below chart is basically your family tree. It even allows for the placement of the family of the spouse.
Running diagonally (only top left towards bottom right) from any box in the table are people of the same generation. They are either a spouse, a sibling, or a cousin.
Running up and down from any box in the table (except Aunt/Uncle-in-law) are people who are in a parent/child relationship.
Note: Cousin has no breakdown for gender such as Sibling = brother/sister, Child = son/daughter, Parent = mother/father.
Plug your name into the appropriate box. Then add the names of your various relatives. Once the needed names are given, you can see how each person is related to you.