How to read and fill in a pedigree chart

The pedigree chart is the oldest and tidiest tool in genealogy. It looks in one direction only, at your ancestors, and gives each of them a fixed number. Once you understand the system, you can find your way around any pedigree chart or ahnentafel list and tell from a single number who is meant. This article explains how the numbering works, what pedigree collapse is and how to fill in a chart properly.

Pedigree chart, family tree, descendant chart, fan chart: which is which?

• Pedigree chart: it starts with one person, the subject, and shows their parents, grandparents, great-grandparents and so on. Siblings, aunts and uncles do not appear. Each generation doubles: 2 parents, 4 grandparents, 8 great-grandparents. In German this is the Ahnentafel.
• Family tree: the everyday word for any diagram of a family, whether it shows ancestors, descendants or both.
• Descendant chart: it starts with a person or a couple and shows all their descendants, through sons and daughters alike. It is the mirror image of the pedigree chart and works well for family reunions.
• Fan chart: a pedigree chart arranged as a half or full circle. The subject sits in the centre and each generation forms a ring. The content is the same as a pedigree chart, just more compact.

Alongside the chart there is the ahnentafel in the narrower English sense: the same people as a numbered list, generation by generation. It is handy once your research goes back so far that no sheet of paper is big enough. A family group sheet, by contrast, covers one couple and their children.

Ahnentafel numbering

The numbering system is old. Michael Eytzinger used it in 1590, the Franciscan friar Jerónimo de Sosa in 1676, and the genealogist Stephan Kekulé von Stradonitz popularised it in 1898 with his Ahnentafel-Atlas. That is why it goes by several names: ahnentafel numbering, the Sosa-Stradonitz system or, in German, Kekulé numbering. The rules are simple:

• The subject is number 1.
• The father of a person with number n is 2n, the mother is 2n + 1.
• The child in the direct line is n / 2, rounded down: 13 is a parent of 6, and so is 12.
• Even numbers are men, odd numbers are women. The only exception is number 1, because the subject can be either.
• A couple always has the numbers n and n + 1, with n even: 4 and 5, 12 and 13.
• The generation is ⌊log₂ n⌋ + 1. Put more simply, generation g covers the numbers from 2^g−1 to 2^g − 1. The great-grandparents (generation 4) are 8 to 15, the great-great-grandparents 16 to 31.

To work out who number 13 is, go backwards: 13 is odd, so a woman, and the mother of 6. Number 6 is even, so the father of 3. Number 3 is the mother of 1. So 13 is your mother’s father’s mother. Here are the first 15 numbers:

A complete pedigree chart of four generations therefore has 15 boxes, one of five generations 31. In general it is 2^g − 1 people for g generations, including the subject.

Pedigree collapse: when ancestors appear twice

On paper, the number of ancestors doubles with every generation. Thirty generations back, you would have more than a billion people in a single generation, more than were alive in the whole world at the time. The arithmetic works out because many ancestors are related to you along more than one path. This is called pedigree collapse, or implex.

An example: if your parents are first cousins, they share a pair of grandparents. That couple appears twice in your pedigree chart, for instance as 8 and 9 and again as 12 and 13. Instead of eight different great-grandparents you then have only six. In small villages and remote regions where people married within a few families for centuries, pedigree collapse is entirely normal and often shows up after only a few generations.

For your chart this means that the person keeps every number the rules give them. At the higher number you write a cross-reference such as “= 8” and do not continue the line there, because the ancestors are already recorded under the lower number.

How to fill in a pedigree chart

Each box takes the same basic facts: the full name with all given names (for women the maiden name, not the married name), birth or baptism, marriage, death or burial, each with date and place, and the occupation where known. Space is tight, so standard abbreviations are used:

• b. born (in European records often *)
• bap. or chr. baptised or christened (~)
• m. married (⚭)
• div. divorced (⚮)
• d. died (†)
• bur. buried (□)

An entry might read: “Anna Maria Smith, b. 12 Mar 1871 Ashford, m. 4 May 1893 same place, d. 2 Jan 1940 Leeds”. Record a baptism date as a baptism, not as a birth, even when the two are often only a few days apart. Anyone checking later will know which event the source actually names.

For dates, the usual genealogy style is day, month, year with the month written out or abbreviated (“12 Mar 1871”), which avoids the 03/04 confusion between American and European formats. Mark uncertain dates clearly: “abt. 1850”, “bef. 1850”, “aft. 1850” or “bet. 1848 and 1852”. GEDCOM files use the same idea with ABT, BEF, AFT and BET … AND. For places, give the name at the time of the event, from small to large (town, county, state or country), and add today’s name where it has changed.

Most important of all: the source. Note where every fact comes from, for example “St John’s parish register, baptisms 1871, no. 34” or “death certificate, Leeds 1940”. Many printed forms have no field for it. In that case, number your sources on a separate sheet and write only the source number in the box.

More than four generations: continuation charts

One sheet usually holds four generations. For the ancestors of your great-grandparents you start continuation charts: a new chart begins with, say, number 8 from your first chart as its starting person, with a note such as “No. 1 on this chart is no. 8 on chart 1”. To keep things straight, also write each person’s number in your overall ahnentafel count next to them. The rules carry on unchanged: the father of 8 is 16, the mother 17. That way every person stays easy to find, however many sheets your research grows to.

Templates, software and GEDCOM

To print and fill in by hand, we offer free printable charts, among them a 4-generation pedigree chart with 15 boxes and a 5-generation fan chart whose 31 boxes already carry the ahnentafel numbers. If you are just getting started, our guide How to make a family tree, step by step helps with the first conversations and records.

Once you have more than a few dozen people, genealogy software is more convenient. Many programs assign ahnentafel numbers automatically and print ahnentafel reports at the click of a button. Make sure you can export your data as a GEDCOM file. What such a file contains, and why it is the shared exchange format of genealogy, is covered in What is a GEDCOM file?

Your pedigree chart as a poster

If you would like your pedigree on the wall, you can design it as a poster with us. Modern Clean is laid out like a classic pedigree chart, with descendants below if you wish. Heritage Fan arranges your ancestors as a fan chart, and Heritage Oak places them in a painted tree. Upload your GEDCOM file or enter your family in the online wizard, and you will see a preview before you order. Design your pedigree chart.