Ahnentafel Conventions

Excerpts from online encyclopedias:

An Ahnentafel is a list of one's ancestors with each one numbered in a sequential manner that makes it easy to calculate relationships. The Ahnentafel method is the most common method of numbering ancestors.

Ahnentafel is a German word that translates as “ancestor table” or, literally, a list of one’s ancestors. The same numbering system is sometimes called the Sosa-Stradonitz System, named after the Spanish genealogist Hieronymus/Jerome de Sosa, who first used it in 1676, and after the German genealogist Stephan Kekulé von Stradonitz [1863-1933], who popularized it in his 1896 Ahnentafel Atlas.

In an Ahnentafel numbering system, the proband is assigned the number one. The father of each person is assigned a number equal to double the child’s number. The mother of each person is assigned a number equal to double the child’s number plus one. As a result, the number of any child is one-half that of their parent, ignoring any remainder. For the first four generations, the numbers assigned a given person and their ancestors are reflected in the table below.

Translating this to a real person, here is an excerpt from the Ahnentafel of one well-known American, complete with Ahnentafel numbers:

  1. George Walker Bush, b. New Haven, Conn., 6 July 1946, m. 5 Nov. 1977, Laura Lane Welch
  2. George Herbert Walker Bush, b. Milton, Mass., 12 June 1924, m. Rye, N.Y., 6 Jan. 1945
  3. Barbara Pierce
  4. Prescott Sheldon Bush, b. Columbus, Ohio, 15 May 1895, m. Kennebunkport, Maine, 6 Aug. 1921, d. New York, N.Y., 8 Oct. 1972
  5. Dorothy Walker, b. near Walker's Point, York Co., Me., 1 July 1901, d. Greenwich, Conn., 19 Nov. 1992
  6. Marvin Pierce, b. Sharpsville, Pa., 17 June 1893, m. Aug. 1918, d. Rye, N.Y., 17 July 1969
  7. Pauline Robinson, b. Ohio, April 1896, d. Rye, N.Y., 23 Sept. 1949
  8. Samuel Prescott Bush, b. Brick Church, N.J., 4 Oct. 1863, m. Columbus, Ohio, 20 June 1894, d. Columbus, Ohio, 8 Feb. 1948
  9. Flora Sheldon, b. Franklin Co., Ohio, 17 Mar. 1872, d. "Watch Hill", R.I., 4 Sept. 1920
  10. George Herbert Walker, b. St. Louis, Mo., 11 June 1875, m. St. Louis, Mo., 17 Jan. 1899, d. New York, N.Y., 24 June 1953
  11. Lucretia [Loulie] Wear, b. St. Louis, Mo., 17 Sept. 1874, d. Biddeford, Me., 28 Aug. 1961
  12. Scott Pierce, b. Sparkville, Pa., 18 Jan. [or June?] 1866, m. 26 Nov. 1891
  13. Mabel Marvin, b. Cincinnati, Ohio, 4 June 1869
  14. James Edgar Robinson, b. near Marysville, Oh., 15 Aug. 1868, m. Marion Co., Ohio, 31 March 1895, d. 1931
  15. Lula Dell Flickinger, b. Byhalia, Ohio, March 1875

The primary disadvantage of Ahnentafel numbers is that the size of each number when going back many generations becomes quite large. Someone with a documented line of descent from Charlemagne may be using Ahnentafel numbers in the billions.

Ahnentafel Conventions
Ahnentafel Binary Relation to Self F & M Atree Gen APG
1 1 Self proband 1 Self
2 10 father proband's father 2 2
3 11 mother proband's mother 2 2
4 100 paternal grandfather proband's father's father 3 4
5 101 paternal grandmother proband's father's mother 3 4
6 110 maternal grandfather proband's mother's father 3 4
7 111 maternal grandmother proband's mother's mother 3 4
8 1000 paternal great grandfather proband's father's father's father 4 8
9 1001 paternal great grandmother proband's father's father's mother 4 8
10 1010 paternal great grandfather proband's father's mother's father 4 8
11 1011 paternal great grandmother proband's father's mother's mother 4 8
12 1100 maternal great grandfather proband's mother's father's father 4 8
13 1101 maternal great grandmother proband's mother's father's mother 4 8
14 1110 maternal great grandfather proband's mother's mother's father 4 8
15 1111 maternal great grandmother proband's mother's mother's mother 4 8

Ahnentafel Conversions by Danny Jones

Ahnentafel number:
Binary: F & M: Generation: APG:
Binary number:
Ahnentafel: F & M: Generation: APG:
F & M representation:
Binary: Ahnentafel: Generation: APG:

ahnentafel horizontal