Cousin Relationships Explained
Ever heard “he’s my second cousin twice removed” and wondered what that actually means? You may remember Pippin explaining exactly how he’s related to Frodo in The Lord of the Rings, while everyone else’s eyes glazed over.
Cousin talk gets confusing fast: “eighth cousin once removed,” half cousins, double cousins. But the system is actually simple once you’ve seen a few examples. Diagrams help me, so that’s what we’ve included here.
It all starts with a common ancestor
“Second cousin twice removed” describes how two people are related through an ancestor they share, such as a great-grandparent. Two numbers do all the work:
- The degree (first, second, third cousin) tells you how many generations separate the closer of you from the common ancestor.
- The removal (once, twice removed) tells you how many generations apart you and your cousin are from each other.
My head hurts already. Let’s look at some pictures.
Finding the degree
Count the generations between you and the common ancestor, then do the same for your cousin. Whoever is closer to the ancestor sets the degree.
Grandchildren of the same grandparents are first cousins. Great-grandchildren of the same great-grandparents are second cousins. Great-great-grandchildren are third cousins, and so on.
Finding the removal
If you and your cousin are the same number of generations from the common ancestor, there’s no “removed.” If you’re not, the difference is the removal.
In this example, one cousin is two generations further from the common ancestor than the other, so they’re second cousins twice removed.
A quick cousin chart
Find how you are related to the common ancestor down the left side, and how your relative is related across the top. The box where they meet is your relationship.
| Their relationship to the common ancestor → Yours ↓ | Child | Grandchild | Great-grandchild | 2nd great-grandchild |
|---|---|---|---|---|
| Child | Sibling | Niece or nephew | Grandniece or nephew | Great-grandniece or nephew |
| Grandchild | Niece or nephew | First cousin | First cousin once removed | First cousin twice removed |
| Great-grandchild | Grandniece or nephew | First cousin once removed | Second cousin | Second cousin once removed |
| 2nd great-grandchild | Great-grandniece or nephew | First cousin twice removed | Second cousin once removed | Third cousin |
Examples in plain English
First cousins
The children of your aunts and uncles are your first cousins. You share a set of grandparents, one generation up from your parents.
Second cousins
Your child and your first cousin’s child are second cousins. They share great-grandparents.
First cousin once removed
Your parent’s first cousin is your first cousin once removed. So is your first cousin’s child. In both cases you’re one generation apart.
Half cousins
If your parents are half-siblings (they share only one parent), you and their children are half first cousins: you share one grandparent instead of two.
Double cousins
When two siblings from one family marry two siblings from another, their children are double first cousins. They share all four grandparents and about as much DNA as half-siblings.
Cousins and DNA
If you’ve taken a DNA test, your match list is full of cousins. The testing company will estimate a relationship, such as “2nd–4th cousin,” based on how much DNA you share, measured in centimorgans (cM). Because DNA is inherited somewhat randomly, the same amount of shared DNA can fit several relationships. The free Shared cM Project tool from DNA Painter shows the possibilities for any amount, and comparing family trees with your match usually settles it.
Let the computer do the math. FamilySearch Family Tree and Ancestry both show exactly how you’re related to anyone in your tree, step by step, all the way back to your common ancestor.
So the next time someone at a reunion says “we’re second cousins once removed,” you’ll know exactly what they mean. Pippin would be proud.