The first ahnentafel, published by Michaël Eytzinger in Thesaurus principum hac aetate in Europa viventium Cologne: 1590, pp. 146-147, in which Eytzinger first illustrates his new functional theory of numeration of ancestors; this schema showing Henry III of France as n° 1, de cujus, with his ancestors in five generations. The remainder of the volume shows 34 additional schemas for rulers and princes of Europe using his new method.


An ahnentafel (German for "ancestor table"; German: [ˈʔaːnənˌtaːfəl]) or ahnenreihe ("ancestor series"; German: [ˈʔaːnənˌʁaɪə]) is a genealogical numbering system for listing a person's direct ancestors in a fixed sequence of ascent. The subject (proband) of the ahnentafel is listed as #1, the subject's father as #2 and the mother as #3, the paternal grandparents as #4 and #5 and the maternal grandparents as #6 and #7, and so on, back through the generations. Apart from #1, who can be male or female, all even-numbered persons are male, and all odd-numbered persons are female. In this schema, the number of any person's father is double the person's number, and a person's mother is double the person's number plus one. Using this knowledge of numeration, one can derive some basic information about individuals who are listed without additional research.


This construct displays a person's genealogy compactly, without the need for a diagram such as a family tree. It is particularly useful in situations where one may be restricted to presenting a genealogy in plain text, for example, in e-mails or newsgroup articles. In effect, an ahnentafel is a method for storing a binary tree in an array by listing the nodes (individuals) in level-order (in generation order).

Other names[]

The ahnentafel system of numeration is also known as: the Eytzinger Method, for Michaël Eytzinger, the Austrian-born historian who first published the principles of the system in 1590;[1] the Sosa Method, named for Jerónimo (Jerome) de Sosa, the Spanish genealogist who popularized the numbering system in his work Noticia de la gran casa de los marqueses de Villafranca in 1676;[2] and the Sosa–Stradonitz Method, for Stephan Kekulé von Stradonitz, the genealogist and son of Friedrich August Kekulé, who published his interpretation of Sosa's method in his Ahnentafel-atlas in 1898. An ahnentafel list is sometimes called a "Kekulé" after Stephan Kekulé von Stradonitz.[3]

"Ahnentafel" is a loan word from the German language, and its German equivalents are Ahnenreihe and Ahnenliste. In German, Ahnentafel has the broader meaning a pedigree chart with no specific need for numbering.

Inductive reckoning[]

To find out what someone's number would be without compiling a list, one must first trace how they relate back to the subject or person of interest, meaning one records that someone is the subject's father's mother's mother's father's father's... Once one has done that, one can use two methods.

First method[]

Use the knowledge that a father's number will be twice that individual's number, or a mother's will be twice plus one, and just multiply and add 1 accordingly. For instance, someone can find out what number Electress Sophia of Hanover would be on an ahnentafel of Peter Mark Andrew Phillips. Sophia is Peter's mother's mother's father's father's father's mother's father's father's father's father's father's mother. So, we multiply and add:

1×2 + 1 = 3
3×2 + 1 = 7
7×2 = 14
14×2 = 28
28×2 = 56
56×2 + 1 = 113
113×2 = 226
226×2 = 452
452×2 = 904
904×2 = 1808
1808×2 = 3616
3616×2 + 1 = 7233

Thus, if we were to make an ahnentafel for Peter Phillips, Electress Sophia would be #7233.

Second method[]

This is an elegant and concise way to visualize the genealogical chain between the subject and the ancestor.

1. Write down the digit "1", which represents the subject, and, writing from left to right, write "0" for each "father" and "1" for each "mother" in the relation, ending with the ancestor of interest. The result will be the binary representation of the ancestor's ahnentafel number. Using the Sophia example, there is a translation of the chain of relations into a chain of digits.

Sophia = Peter's mother's mother's father's father's father's mother's father's father's father's father's father's mother
Sophia = 1110001000001

2. If needed, convert the ahnentafel number from its binary to its decimal form. A conversion tool might prove handy.

Sophia = 1110001000001
Sophia = 7233

Deductive reckoning[]

We can also work backwards and find what the relation is from the number.

Reverse first method[]

  1. One starts out by seeing if the number is odd or even.
  2. If it is odd, the last part of the relation is "mother," so subtract 1 and divide by 2.
  3. If it is even, the last part is "father," and one divides by 2.
  4. Repeat steps 2–3, and build back from the last word.
  5. Once one gets to 1, one is done.

On an ahnentafel of HRH The Duke of Cambridge, Mr John Wark is number 116. We follow the steps:

116/2 = 58 58/2 = 29 29 − 1 = 28 and 28/2 = 14 14/2 = 7 7 − 1 = 6 and 6/2 = 3 3 − 1 = 2 and 2/2 = 1
father father mother father mother mother

We reverse that, and we get that #116, Mr John Wark, is Prince William's mother's mother's father's mother's father's father.

Reverse second method[]

1. Convert the ahnentafel number from decimal to binary.

Mr John Wark = 116
Mr John Wark = 1110100

2. Replace the leftmost "1" with the subject's name and replace each following "0" and "1" with "father" and "mother" respectively.

Mr John Wark = 1110100
Mr John Wark = Prince William's mother's mother's father's mother's father's father
decimal binary relation
1 1 proband
2 10 father
3 11 mother
4 100 paternal grandfather
5 101 paternal grandmother
6 110 maternal grandfather
7 111 maternal grandmother
8 1000 father's father's father
9 1001 father's father's mother
10 1010 father's mother's father
11 1011 father's mother's mother
12 1100 mother's father's father
13 1101 mother's father's mother
14 1110 mother's mother's father
15 1111 mother's mother's mother

Calculation of the generation number[]

The number of the generation can be calculated from any Kekulé number with the logarithm base 2. It is assumed that generation zero (0) represents the initial person (Kekulé number 1).

 log2(<Kekulé number>)
 -> The result needs to be rounded down to a full integer (truncate decimal digits)
 = generation number


For an example, see William, Duke of Cambridge (1982)/ancestors

Other German definitions[]

Ahnentafel of Sigmund Christoph von Waldburg-Zeil-Trauchburg

Ahnentafel published as an Ariernachweis

European nobility took pride in displaying their descent. In the German language, the term "Ahnentafel" may refer to a list of coats of arms and names of one's ancestors, even when it does not follow the numbered tabular representation given above. In this case the German "Tafel" is taken literally to be a physical "display board" instead of an abstract scheme.

In Nazi Germany, the Law for the Restoration of the Professional Civil Service required a person to prove non-Jewish ancestry with an Ariernachweis (Aryan certificate). The certificate could take the form of entries in the permanent Ahnenpass (that was sorted according to the ahnentafel numbering system) or as entries in a singular Arierschein (Aryan attestation) that was titled "Ahnentafel".


See also[]


  1. ^ Eytzinger, Michael, Thesaurus principum hac aetate in Europa viventium, quo progenitores eorum... simul ac fratres et sonores inde ab origine reconduntur... usque ad annum..., Cologne: G. Kempensem, 1590 (1591). Note: In commentaries, his surname may appear in variant forms, including: Aitsingeri, Aitsingero, Aitsingerum, Eyzingern.
  2. ^ Jouniaux, Léo, Généalogie : pratique, méthode, recherche, Quercy: Seuil, 2006, pp. 44–45.
  3. ^ Kekulé von Stradonitz, Stephan, Ahnentafel-atlas. Ahnentafeln zu 32 Ahnen der Regenten Europas und ihrer Gemahlinnen, Berlin: J. A. Stargardt, 1898–1904. This volume contains 79 charts of the sovereigns of Europe and their wives.

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