The Ahnentafel system

Have you come across the Ahnentafel genealogical numbering system?

‘Ahnentafel’, meaning ‘ancestor table’ in German, is an ascending numbering system for ordering and identifying ancestors.  Starting with the Subject of the tree (i.e. you, or the person/ descendant whose ancestry is being shown) and working backwards, every direct ancestor is given a number.  The Subject is number 1, his/her father is 2, mother is 3, paternal grandfather 4, paternal grandmother 5, maternal grandparents 6 and 7, and so on.

A quick Internet search will return many examples of Ahnentafel templates and charts, some circular, some with colours, some completed, for example with the royal family’s details, some looking very much like a regular pedigree chart but with the addition of numbers….  This one from Lost Cousins is the one that introduced me to Ahnentafel in the first place.

The features of the Ahnentafel chart are:

  • It starts with a Subject / descendant and works backwards through the generations
  • It shows only the direct line – no siblings, no other children
  • Apart from the Subject – number 1 on the chart, who may be male or female – the direct male ancestors are always even numbers and the direct female ancestors are always odd numbers

Calculating each ancestor’s number
Thanks to the elegance of mathematics, the correct number can easily be allocated to an ancestor, even if they are many generations in the past, simply by following this simple formula:

  • To obtain any person’s father’s number, anywhere on your ancestry, double that younger person’s number.
  • To obtain any person’s mother’s number, double their own number as above, then add 1 to that figure.  The mother will therefore always be one number higher than the father.

You are number 1
Your mother is number 3   [1×2 =2 +1 =3]
Her father (your grandfather) is 3×2 =6 and her mother (your maternal grandmother) is 3×2 =6 +1 =7
Your maternal grandmother’s mother (your mother’s mother’s mother) is therefore 7×2 =14 +1 =15
Your mother’s mother’s mother’s father is therefore 15×2 =30.
His father is 60.  His father is 120 and the mother is 121, and so on.

This arrangement of numbers of course applies to everyone’s tree in the same way.  But be aware if you’re working on your cousin’s tree that the arrangement of numbers will not necessarily be the same.  If your cousin is the child of your mother’s brother, your maternal grandparents will be your cousin’s paternal grandparents.  In other words, although half of your trees will be identical, the arrangement on the Ahnentafel will be completely different.

As you see, using this system, provided you have already calculated the Ahnentafel number of the closer generation (which you will, since we always work back through time), then you can always work out very easily the Ahnentafel number of that ancestor’s parents.

Generation numbers
We have 2 parents, 4 grandparents, 8 great grandparents, 16 GG grandparents, and so on.  The number of direct ancestors doubles with each generation.  To make it easier to see at a glance in which generation an ancestor is located we can choose to include a prefix to the Ahnentafel number.  In the worked example above, my mother’s mother’s mother’s father is 30.  As my GG grandfather he comes within the fifth generation, and I could therefore indicate him with the reference number 5: 30 instead of just with the A-number 30.

Table showing organisation of generations by Ahnentafel numbers

Why would you use this system?
It is undoubtedly easier to pinpoint an ancestor at A-number 418 or 9: 418 than to describe him as the subject’s mother’s father’s mother’s father’s father’s father’s mother’s father – or even to use the shorthand of that: MFMFFFMF.  But of course it will only be easier if we’re using it in communication with someone else who understands the system!  You may, like me, be familiar with the glazing over of the eyes of pretty much any family member if you stray too far into the detail of a fascinating (obviously!) ancestral tale.  I know that if I started to refer to my ancestors using numerical code or possibly worse, using long strings of M’s and F’s, those glazed expressions would quickly transform into something questioning my sanity.  Generally speaking, ‘my 6x great grandfather’ will more than suffice!

Even on paper, because of the doubling of ancestors that must be squeezed onto the page with every new generation, there’s a limit to how many generations can be included on one page.  Even if you’re able to print out on A3 paper, the sheer numbers of ancestors to fit in the additional columns will mean only a couple of extra generations at most can be added.  The Lost Cousins example linked to above includes 3xG grandparents (six generations total), requiring space for 32 names in the final column.  Two more generations would require space for 128 5xG grandparents in that final column – and I have identified several 10x and 12x great grandparents!

The above problems can of course be overcome by effectively starting a new table, appropriately re-numbered, at each 3xG grandparent.  This would get you back to eleven generations, or your 8xG grandparents and would be less unwieldy.  In this way, I find Ahnentafel a useful system to include in a printed family history, making it easy to pinpoint certain ancestors when interesting stories emerge.  However, I have also adapted Ahnentafel in my own information organisation system.  I’ll write about that in my next post.