What is a 3rd great-grandparent?
Short answerYour 3rd great-grandparent is your 2nd great-grandparent’s parent. You are their 3rd great-grandchild. A 3rd great-grandparent is a direct-line ancestor, 5 generations above you. You inherit about 3.12% of your DNA from each 3rd great-grandparent on average.
The family line, drawn out
Follow the highlighted line from you up to the shared ancestor and down to them.
How to work it out
Count the generations straight up: parent is 1, grandparent 2, great-grandparent 3. A 3rd great-grandparent is 5 up. From 2nd great-grandparent on, genealogists number the “greats” to keep them readable: a 3rd great-grandparent is a great-great-great-grandparent.
Everyone has 32 3rd great-grandparents by birth, 16 on each parent’s side, unless the same person appears twice in the tree (cousins who married, which genealogists call pedigree collapse). Family Trees always takes the shortest line, so someone who is both a grandparent and a great-grandparent reads as grandparent.
What to call each other
| Them, to you | You, to them | |
|---|---|---|
| Female | 3rd great-grandmother | 3rd great-granddaughter |
| Male | 3rd great-grandfather | 3rd great-grandson |
| Anyone | 3rd great-grandparent | 3rd great-grandchild |
Their family and yours
Relationships shift by one step for each generation. Here is how the people around them relate to you:
| Their other children (not on your line) | 3rd great-aunt or uncle |
| Your child sees them as your child’s | 4th great-grandparent |
| Your parent sees them as your parent’s | 2nd great-grandparent |
| What they call you | 3rd great-grandchild |
Shared DNA
On average, you inherit about 3.12% of your DNA from a 3rd great-grandparent. That figure is the expected value: it halves with every generation of separation, and real amounts vary from person to person.
Let Family Trees name it for you
In Family Trees, open anyone’s page to see how they are related to you in plain words, or choose any two people under How are they related?. The app counts the shortest blood line through birth and adoptive parents, names step, foster and in-law relations too, and uses exactly the words on this page. It’s free for a family of up to 100 people. You can also try the relationship calculator here.
Questions
What is a 3rd great-grandparent?
Your 3rd great-grandparent is your 2nd great-grandparent’s parent. You are their 3rd great-grandchild.
How many 3rd great-grandparents do I have?
Everyone has 32 3rd great-grandparents by birth, 16 on each side, unless an ancestor appears twice because relatives married each other.
How much DNA do you share with a 3rd great-grandparent?
About 3.12% on average. Each generation of separation halves the expected amount, and individual results vary.
What is my 3rd great-grandparent’s child to me?
Your 3rd great-aunt or uncle, on the same line.