🌲 Number of Ancestors at Generation N Calculator

Every generation back doubles your theoretical number of ancestor slots — 2 parents, 4 grandparents, 8 great-grandparents, and so on (2 raised to the generation number). In practice, actual distinct ancestors are often fewer due to pedigree collapse (shared ancestors appearing more than once in a tree).

Generations back

Doubling, generation by generation

Two parents, four grandparents, and a factor of two for every further step back. The tool lists every row up to the generation you ask for, naming each one, and accepts 1 to 30:

slots at generation n = 2^n

 3  Great-grandparents        8
 5  3x great-grandparents    32
10  8x great-grandparents  1,024
20 18x great-grandparents  1,048,576

The default of 5 returns 32 slots and labels them 3x great-grandparents. Note the naming step: generations 1 to 3 are parents, grandparents and great-grandparents, and from generation 4 the tool switches to the numbered form, so generation 4 is 2x great-grandparents rather than great-great-grandparents.

Genealogical slots versus genetic ancestors

Every slot is a real person, but you did not inherit DNA from all of them. Each generation of inheritance introduces only around thirty crossover points, so your autosomes are a mosaic of a few hundred ancestral pieces at most:

By generation 10 there are 1,024 slots and nowhere near that many pieces to go round, so a large share of those ancestors left you nothing measurable.
A DNA match confirms a line, not the whole row. Finding no shared DNA with a documented 5th cousin is normal and is not evidence the paper trail is wrong.

Distinct people run below the slot count from the moment any cousins marry, and endogamy makes that the rule rather than the exception. In a community that married within itself, one ancestor can fill dozens of slots, which also inflates the shared cM between distant relatives.

Frequently asked questions

How many 3x great-grandparents does a person have?

32, at generation 5. The next row up, 4x great-grandparents, holds 64, and each further step doubles again.

Do I carry DNA from all 1,024 ancestors ten generations back?

No. Recombination cuts your genome into a limited number of blocks, so past roughly seven generations you carry nothing at all from many documented ancestors.

Why does the calculator stop at 30 generations?

Because the figure stops meaning anything. Generation 30 gives 1,073,741,824 slots, far more people than were alive at the time, so beyond that the doubling rule only measures repeated ancestors.