Family relationship calculator
How is a second cousin different from a first cousin once removed? Find the closest ancestor two people share, count the generations from each of them up to that ancestor, and the name follows. The calculator uses the same relationship engine as the editor’s relationship finder.
The interactive calculator needs JavaScript. The table below gives the same answers.
Relationship table
Read across from what the shared ancestor is to person A, and down from what they are to person B. The cell is what B is to A. Generated from the same rules as the calculator.
| Ancestor is B’s… / A’s… | Parent | Grandparent | Great-grandparent | Great-great-grandparent | 3× great-grandparent |
|---|---|---|---|---|---|
| Parent | Sibling | Aunt or uncle (parent’s sibling) | Great-aunt or uncle | Great-great-aunt or uncle | 3× great-aunt or uncle |
| Grandparent | Niece or nephew (sibling’s child) | First cousin | First cousin once removed | First cousin twice removed | First cousin 3 times removed |
| Great-grandparent | Grandniece or nephew | First cousin once removed | Second cousin | Second cousin once removed | Second cousin twice removed |
| Great-great-grandparent | Great-grandniece or nephew | First cousin twice removed | Second cousin once removed | Third cousin | Third cousin once removed |
| 3× great-grandparent | Great-great-grandniece or nephew | First cousin 3 times removed | Second cousin twice removed | Third cousin once removed | Fourth cousin |
Cousins and “removed”, explained
The cousin number is one less than the smaller generation count. Two people who share grandparents (2 and 2) are first cousins; who share great-grandparents (3 and 3), second cousins.
“Removed” is the difference between the two counts. Your first cousin’s child is your first cousin once removed: you are 2 generations from the shared grandparents and they are 3.
Half relationships come from sharing only one of the two ancestors, for example a parent’s child from another marriage is a half sibling, and that half sibling’s child is your half niece or nephew.
Beyond blood relatives
Partners, in-laws and step-relatives are not counted by generations. In the editor, the relationship finder also explains those, for example “sister-in-law (wife’s sister)”, shows the exact path between the two people, and says when a missing parent makes the answer uncertain. Adoptive and foster links are included and labelled.
Common relationships at a glance
- Your parent’s sibling is your aunt or uncle; their parent’s sibling is your great-aunt or great-uncle.
- Your aunt’s or uncle’s child is your first cousin; their child is your first cousin once removed.
- Your parent’s first cousin is also your first cousin once removed, one generation up instead of down.
- Your first cousin’s grandchild is your first cousin twice removed. Your child and your first cousin’s child are second cousins.
- Your grandparent’s first cousin is your first cousin twice removed.
To see these on a real family, open the example family or record your own in the family tree maker.
Cousin and relationship questions
What is a second cousin?
Second cousins share great-grandparents but not grandparents. Your parent’s first cousin’s child is your second cousin.
What does “once removed” mean?
“Removed” means the two cousins are in different generations. Your first cousin’s child is your first cousin once removed, and so is your parent’s first cousin. “Twice removed” is two generations apart.
Is my cousin’s child my niece or nephew?
No. Your first cousin’s child is your first cousin once removed. Nieces and nephews are the children of your brothers and sisters.
What do I call my parent’s cousin?
Your parent’s first cousin is your first cousin once removed. In everyday speech many families call them aunt or uncle, which is fine; the genealogical term is cousin once removed.
What is a double cousin?
Double first cousins share both sets of grandparents, for example when two brothers marry two sisters. They are related through both of their parents, and the editor’s relationship finder shows both paths.
Are second cousins related by blood?
Yes. Second cousins share a pair of great-grandparents, so they are blood relatives, though more distantly than first cousins. Relationships through marriage, such as in-laws, are not blood relationships.