What is a third cousin?
A third cousin shares a set of great-great-grandparents with you. Your parents are second cousins to each other, and your grandparents were first cousins.
Preset to this relationship. Change the steps to compare with neighbouring relationships.
They are your
third cousin
Common ancestors: your great-great-grandparents. Expected shared DNA: 0.781%
Shorter branch = 4 steps → 4 − 1 = 3 → third cousin. Branches differ by 0 → not removed.
Third cousins share about 0.78% of their DNA on average (1/128).
Because shared DNA shrinks by half each generation, a small share of genuine third cousins share no detectable DNA at all in consumer tests — the relationship is still real on paper.
Most people have a surprisingly large number of third cousins, often well over a hundred, which is why they appear so often in DNA match lists.
To check a real pair of relatives, add them to the family tree maker and use How related?, or look them up on the cousin chart.
Questions
Is a third cousin considered family?
Genealogically, yes. You share great-great-grandparents.
What is my third cousin's child to me?
Your third cousin once removed.