Genealogical Numbering Systems

During a meeting with a distant cousin, I was provided with a 94-page report of everyone I was related to on my father’s paternal side that went back seven generations. Each person was assigned a specific number that served as a sort of index.

At first, I didn’t understand this index but I later looked up numbering systems and learned there are a few types used in genealogy.

Register Genealogical Numbering System

The Register Genealogical Numbering System was created in 1870 by the New England Historic Genealogical Society. This numbering system uses both common numerals (1, 2, 3, 4, etc.) and Roman numerals (i, ii, iii, iv, etc.).

In this system, generations are grouped separately.

First Generation 

1 Original Person

2     i Child

ii Child (no children)

iii Child (no children)

3     iv Child

Second Generation

2     Child

i Grandchild (no children)

ii Grandchild (no children)

3     Child

4     i Grandchild

Third Generation

4      Grandchild

5      i Great-grandchild

ii Great-grandchild (no children)

6    iii Great-grandchild

7     iv Great-grandchild

My report utilized this system. It was 94 pages because it outlined every known person in my family tree. With the large page count, I found it necessary to quickly figure out the index numbering system so I could find people within the document quickly and without too much confusion. Once I figured out the numbering system, I was easily flipping through the pages to where a section for specific person started.

SOSA Genealogical Numbering System

Another numbering system that is one of the more popular systems is the SOSA Genealogical Numbering System. This is also known as Ahnentafel, German for “ancestor table”.

The SOSA Genealogical Numbering System numbers of ancestors beginning with a certain person or descendant in the family tree. In this system, a person determines an ancestor’s relationship based on their number (1, 2, 3, 4, etc.).

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. The beginning person is 1. That person’s father is 2 (doubled) and the mother is 3 (doubled plus 1).

Below shows the first 15 numbers that identifies individuals in four generations.

First Generation
1 – Beginning PersonGenealogical Numbering Systems

Second Generation
2 – Father
3 – Mother

Third Generation
4 – Father’s father
5 – Father’s mother
6 – Mother’s father
7 – Mother’s mother

Fourth Generation
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

On a computer, finding people in a long report can be easy by using the Find function (CTRL+F). However, if your document was handwritten, the original computer file has been lost, or it’s a scanned copy and the Find function doesn’t work, it’s important to understand genealogical numbering systems.

Have you ever seen a genealogy or descendant report with a special indexing system to keep the contents organized? Did you know what it was? Did they sound familiar to either of these two systems?

Tell us about your experience with genealogical number systems in the comments!