Ahnentafel number calculator (Kekulé)
Enter an Ahnentafel number, also called a Kekulé or Sosa number, and see who it stands for: line, generation and path from you. Or click your way up through fathers and mothers and read off the number.
Whole number from 1 to 2,097,151
Number 13
maternal great-grandmother
- Who is it?
- mother’s father’s mother
- Generation
- 3 generations back · numbers 8–15 (8 people)
- Sex
- female (odd number)
- Parents of this person
- father · mother
- Child in the line
The calculator runs entirely in your browser: it stores nothing, sends nothing and sets no cookies.
What is an Ahnentafel number?
In an ancestor chart every ancestor gets a fixed number. You, the starting person or proband, are 1, your father is 2, your mother 3, your paternal grandparents 4 and 5, your maternal grandparents 6 and 7. The system is named after Stephan Kekule von Stradonitz, who used it in his Ahnentafel-Atlas of 1898, but it is older: Michael Eytzinger numbered ancestors this way in 1590 and Jerónimo de Sosa in 1676. French and Spanish genealogists therefore say Sosa-Stradonitz, and English speakers often just say Ahnentafel numbers.
The rules in three sentences
The father of person n is 2n, the mother is 2n + 1, and the child in the line is n divided by 2, rounded down. So men have even numbers and women odd ones; only number 1 can be either. Each generation doubles and starts at a power of two.
- Parents: 2 and 3
- Grandparents: 4, 5, 6 and 7
- Great-grandparents: 8 to 15
- 2nd great-grandparents: 16 to 31
- 10 generations back: 1024 to 2047
Reading the path from the number
Without a calculator, work backwards: an even number is a father, an odd one a mother; halve, round down and repeat. 13 is odd, so a mother, namely of 6. 6 is even, a father, namely of 3. 3 is your mother. Read from you outwards, 13 is your mother’s father’s mother, your maternal great-grandmother. In binary you can read it straight off: 13 is 1101, and after the leading 1 each 0 means father and each 1 means mother.
Ahnentafel numbers 1 to 15
The first four generations of the chart, from you to your great-grandparents.
| Number | Path from you | Relationship |
|---|---|---|
| 1 | Starting person (proband) | Starting person (proband) |
| 2 | Father | Father |
| 3 | Mother | Mother |
| 4 | Father’s father | Paternal grandfather |
| 5 | Father’s mother | Paternal grandmother |
| 6 | Mother’s father | Maternal grandfather |
| 7 | Mother’s mother | Maternal grandmother |
| 8 | Father’s father’s father | Paternal great-grandfather |
| 9 | Father’s father’s mother | Paternal great-grandmother |
| 10 | Father’s mother’s father | Paternal great-grandfather |
| 11 | Father’s mother’s mother | Paternal great-grandmother |
| 12 | Mother’s father’s father | Maternal great-grandfather |
| 13 | Mother’s father’s mother | Maternal great-grandmother |
| 14 | Mother’s mother’s father | Maternal great-grandfather |
| 15 | Mother’s mother’s mother | Maternal great-grandmother |
Paternal and maternal lines
In every generation the first half of the numbers belongs to your father’s side and the second half to your mother’s: among the great-grandparents, 8–11 are paternal and 12–15 maternal. The direct male line through fathers only is made of the powers of two (2, 4, 8, 16); the direct female line is 3, 7, 15, 31, always one below the next power of two.
When the same ancestor appears more than once because relatives married each other, genealogists speak of pedigree collapse. That ancestor then carries several numbers. The usual practice is to record the details under the lowest number and refer to it from the others.
Frequently asked questions
What number is my maternal grandmother?
Number 7: your mother (3) times 2 plus 1. Your maternal grandfather is 6.
Why do women have odd numbers?
Because the mother of person n is 2n + 1, which is always odd. Fathers get 2n, which is always even.
How many ancestors are in one generation?
In theory 2 to the power of the generation: 4 grandparents, 8 great-grandparents, 1024 ancestors ten generations back. Because of pedigree collapse, the number of different people is lower in practice.
Are Kekulé, Sosa and Ahnentafel numbers the same?
Yes. It is one numbering system; different countries name it after different people.
Keep going with your chart
- Relationship calculator
How are we related? Name, cousin degree and expected shared DNA.
- Pedigree chart guide
Layout, generations and Ahnentafel numbers explained.
- How to make a family tree
From asking relatives to a finished file.
- Free printable charts
Blank pedigree and fan charts as PDF.
If you like, we can print your ancestor chart as a poster. Design a family tree poster