What cousin is that? A family relationship calculator
Find the nearest ancestor two people share, say what each of them is to that ancestor, and the calculator names the relationship — second cousin, first cousin twice removed, great-aunt. It is the same counting the archive uses to work out how Elizabeth II and Prince Philip, or Victoria and Albert, were related.
The relationship chart
Rows are what the first person is to the shared ancestor, columns what the second person is.
| child | grandchild | great-grandchild | great-great-grandchild | great-great-great-grandchild | 4× great-grandchild | |
|---|---|---|---|---|---|---|
| child | sibling | aunt / uncle | great-aunt / great-uncle | great-great-aunt / great-great-uncle | great-great-great-aunt / great-great-great-uncle | 4× great-aunt / 4× great-uncle |
| grandchild | niece / nephew | 1st cousin | 1st cousin once removed | 1st cousin twice removed | 1st cousin 3 times removed | 1st cousin 4 times removed |
| great-grandchild | great-niece / great-nephew | 1st cousin once removed | 2nd cousin | 2nd cousin once removed | 2nd cousin twice removed | 2nd cousin 3 times removed |
| great-great-grandchild | great-great-niece / great-great-nephew | 1st cousin twice removed | 2nd cousin once removed | 3rd cousin | 3rd cousin once removed | 3rd cousin twice removed |
| great-great-great-grandchild | great-great-great-niece / great-great-great-nephew | 1st cousin 3 times removed | 2nd cousin twice removed | 3rd cousin once removed | 4th cousin | 4th cousin once removed |
| 4× great-grandchild | 4× great-niece / 4× great-nephew | 1st cousin 4 times removed | 2nd cousin 3 times removed | 3rd cousin twice removed | 4th cousin once removed | 5th cousin |
Worked examples from the archive
- Elizabeth II and Prince Philip — Elizabeth II was a great-great-grandchild of Christian IX of Denmark and Louise of Hesse-Kassel, Prince Philip a great-grandchild: Elizabeth II was Prince Philip’s second cousin once removed. Read the story
- Queen Victoria and Prince Albert — Queen Victoria was a grandchild of Francis of Saxe-Coburg-Saalfeld and Augusta Reuss of Ebersdorf, Prince Albert a grandchild: Queen Victoria was Prince Albert’s first cousin. Read the story
- Richard III and Henry VII — Richard III was a great-grandchild of John of Gaunt and Katherine Swynford, Henry VII a great-great-grandchild: Richard III was Henry VII’s second cousin once removed. Read the story
- Agrippina the Younger and Claudius — Agrippina the Younger was a grandchild of Drusus the Elder and Antonia Minor, Claudius a child: Agrippina the Younger was Claudius’s niece. Read the story
How does the calculator work?
Every blood relationship runs through a shared ancestor. Pick what the first person is to that ancestor (a child, a grandchild, a great-grandchild…) and what the second person is to the same ancestor, and the relationship follows from the two counts.
If one person is the ancestor themself, the other is their child, grandchild or further descendant. If both are children of the ancestor, they are siblings; if one is a child and the other a grandchild, they are aunt or uncle and niece or nephew.
What is a second cousin?
First cousins share grandparents; second cousins share great-grandparents; third cousins share great-great-grandparents. Put another way, the children of first cousins are second cousins to each other.
The degree comes from whichever of the two people is fewer generations below the shared ancestor: two generations makes first cousins, three makes second cousins, and so on.
What does “once removed” mean?
“Removed” counts the generations between two cousins. Your first cousin’s child is your first cousin once removed — and so is your parent’s first cousin, since the relationship reads the same in both directions. Two generations apart is twice removed.
Can two people be related in more than one way?
Yes, and in royal families it is the rule rather than the exception. Elizabeth II and Prince Philip were second cousins once removed through Christian IX of Denmark and Louise of Hesse-Kassel, and also third cousins through Queen Victoria and Prince Albert. The usual answer gives the nearest route; the archive shows every one it finds.
What about half cousins and double cousins?
The calculator assumes the shared ancestor is a couple, as it is for most cousins. Half first cousins share only one grandparent — their parents were half-siblings — but the cousin degree and the removal are counted the same way.
Double first cousins share both sets of grandparents, which happens when two siblings marry two siblings from another family. They are first cousins twice over, through each side.