Why and How Ancestors Are Numbered

The numbering system behind our family tree

As a family tree grows — with more and more people and recurring family names — it becomes necessary to file the available information in a logical way.
A family tree usually refers to the graphical depiction of one's lineage, whereas an ancestor list lets you record extensive data on each individual person. In such a list, ancestors are assigned numbers to make relationships clear.

Kekulé — The Numbering System

Kekulé is a logically structured numbering system. Under this system, the starting person (proband) always receives the number 1. A person's father's number is always double the person's own number, and the mother's number is double plus one. As a result, male ancestors always have even numbers, while female ancestors have odd numbers.

Names for the Individual Generations

The various generations have been given names such as great-great-grandparents, 3x-great-grandparents or 4x-great-grandparents. Naming each generation with an ever-longer string of "great-"s would quickly become unwieldy and, after a certain point, impossible to follow. The Kekulé numbers below correspond to the common generation names and degrees of kinship:

Proband
Kekulé number 1

Generation I: Parents
Kekulé numbers 2–3

Generation II: Grandparents
Kekulé numbers 4–7

Generation III: Great-grandparents
Kekulé numbers 8–15

Generation IV: Great-great-grandparents
Kekulé numbers 16–31

Generation V: 3x-great-grandparents
Kekulé numbers 32–63

Generation VI: 4x-great-grandparents
Kekulé numbers 64–127

Generation VII: 5x-great-grandparents
Kekulé numbers 128–255

Generation VIII: 6x-great-grandparents
Kekulé numbers 256–511

Generation IX: 7x-great-grandparents
Kekulé numbers 512–1023

Generation X: 8x-great-grandparents
Kekulé numbers 1024–2047

Generation XI: 9x-great-grandparents
Kekulé numbers 2048–4095

Generation XII: 10x-great-grandparents
Kekulé numbers 4096–8191

Generation XIII: 11x-great-grandparents
Kekulé numbers 8192–16383

There are, of course, plenty more generations and generation names beyond this.
This numbering system, however, has no way of including additional relatives such as siblings. For my paternal grandfather's siblings (Kekulé number 4), for example, I've assigned the numbers 4a, 4b, and so on.

"Only those who care about the present write a chronicle."
(Johann Wolfgang von Goethe)