Genealogical numbering systems

There are several widely adopted genealogical numbering systems for depicting a or  in text format.

Ahnentafel
, also known as the Sosa-Stradonitz system, allows for the numbering of ancestors beginning with a descendant. The system allows one to derive an ancestor's number without compiling the list and allows one to derive an ancestor's relationship based on their number.

The number of a person's father is the double of their own number, and the number of a person's mother is the double of their own, plus one. For instance if the number of John Smith is 10, his father is 20, and his mother is 21.

The first 15 numbers are as follows: 1 self 2 father 3 mother 4 father's father 5 father's mother 6 mother's father 7 mother's mother 8 father's father's father 9 father's father's mother 10 father's mother's father 11 father's mother's mother 12 mother's father's father 13 mother's father's mother 14 mother's mother's father 15 mother's mother's mother

Register Numbering System
The Register Numbering System uses both (1, 2, 3, 4) and  (i, ii, iii, iv). Generations are grouped separately.

The system was created in 1870 for use in the New England Historic and Genealogical Register published by the. Register Style, of which the numbering system is part, is one of two major styles used in the U.S. for compiling descending genealogies. (The other being the NGSQ style.)

NGSQ Numbering System
The NGSQ Numbering System gets its name from the National Genealogical Society Quarterly, which uses the numbering system. It is sometimes called the Record System, or the Modified Register System because it derives from the Register Numbering System.

Henry Numbering System
The Henry Numbering System is a descending system created by. The system begins with 1. The oldest child becomes 11, the next child is 12, and so on. The oldest child of 11 is 111, the next 112, and so on. The system allows one to derive an ancestor's relationship based on their number. For example, 621 is the first child of 62, who is the second child of 6, who is the sixth child of 1.

In the Henry system, when there are more than nine children, X is used for the 10th child, A is used for the 11th child, B is used for the 12th child, and so on. In the Modified Henry system, when there are more than nine children, numbers greater than nine are placed in parentheses.

Henry		         Modified Henry 1. Progenitor 		     1. Progenitor 11. Child		        11. Child 111. Grandchild		    111. Grandchild 112. Grandchild		    112. Grandchild 12. Child		        12. Child 121. Grandchild		    121. Grandchild 122. Grandchild		    122. Grandchild 123. Grandchild		    123. Grandchild 124. Grandchild		    124. Grandchild 125. Grandchild		    125. Grandchild 126. Grandchild		    126. Grandchild 127. Grandchild		    127. Grandchild 128. Grandchild		    128. Grandchild 129. Grandchild		    129. Grandchild 12X. Grandchild		    12(10). Grandchild

d'Aboville System
d'Aboville is a descending system very similar to the Henry system. It differs in that periods are used to separate the generations and no changes in numbering are needed for families with more than nine children. For example:

1 Progenitor 1.1 Child 1.1.1 Grandchild 1.1.2 Grandchild 1.2 Child 1.2.1 Grandchild 1.2.2 Grandchild 1.2.3 Grandchild 1.2.4 Grandchild 1.2.5 Grandchild 1.2.6 Grandchild 1.2.7 Grandchild 1.2.8 Grandchild 1.2.9 Grandchild 1.2.10 Grandchild

This system was developed by Count in  and is widely used in.

de Villiers/Pama System
The de Villiers/Pama System gives letters to generations, and then numbers children in birth order. Therefore c4 is the fourth grandchild and d3 is the third great grandchild. For example:

a Progenitor b1 Child c1 Grandchild d1 Great grandchild d2 Great grandchild c2 Grandchild c3 Grandchild b2 Child c1 Grandchild c2 Grandchild c3 Grandchild

The de Villiers/Pama system is the standard for genealogical works in. It was developed in the by  and used in his three volume Geslachtregister der Oude Kaapsche Familien (Genealogies of Old Cape Families). The system was refined by Dr., one of the founding members of the.

Notes and references

 * About.com: Numbering Your Family Tree
 * Numbering Systems in Genealogy by Richard A. Pence