Family tree diagram. Height is the number of generations back. Width is the number of people in the top generation. Number in generation is 2 to the power of n, where n = the number of generations back.

How Big Is Your Family Tree?

Asking how big your family tree is could seem like a silly question. Everyone has two parents, four grandparents, eight great-grandparents, and so on. We could continue this back for as long as humans have existed and end up with about the same number for everyone.

The question of how big your family tree is becomes more useful when you’re trying to draw it. As soon as you’re adding more than a few generations, drawing a family tree will require some planning. You need to know how big your paper needs to be and how you’ll position people on it.

Long Family Trees

Some family trees are long scrolls of paper tracing back one line of the family for many generations. The tree may include some spouses and switch between the maternal and paternal lines on occasion (usually to follow the more interesting or influential line), but it always remains narrow. If there is enough information, the family line could be traced back for centuries, with the tree getting longer and longer as each generation is added.

Diagram of a family tree showing one line so it is long and narrow.
Focusing on one line (with some spouses included) results in a long family tree. © 2021 TTGS

Wide Family Trees

Most people take a broader approach to genealogy, tracing every line of the family. The number of ancestors in each generation is double that of the generation below. By the time you’re recording your great-great-great-grandparents, you will have 32 names to add, but you’ll only have gone back five generations. If you can get back 10 generations, there will be 1024 ancestors. The tree will become much wider than its height.

Diagram of family tree showing all ancestors.
Adding all ancestors in each generation results in a wide family tree. © 2021 TTGs

What Size Is Your Family Tree?

If you’re making a long family tree for one line of your ancestors, then you just need to know how many generations back you can go. Multiply this number by the amount of space you need to fill in one generation and this is the length of your paper.

If you want to draw a family tree including all your ancestors, then you will also need to calculate how wide the paper should be. To do this, you should work out how many people are in the top generation of the tree. Count the number of generations back you need to go (starting at 1 generation back for the parents of the person at the bottom of the tree). Then raise two to the power of this number. To work out how big your paper needs to be, multiply the result by the amount of space you want to use to write each name.

Family tree diagram. Height is the number of generations back. Width is the number of people in the top generation. Number in generation is 2 to the power of n, where n = the number of generations back.
How to calculate the size of your family tree. © 2021 TTGs

To draw a tree like the one pictured above, you would count three generations back and then calculate 23 = 8 to know there should be eight places in the top generation. If you need 3cm of space to write each name, your paper will need to be 8×3 = 24cm wide.

Planning Your Family Tree

Real family trees can be more complicated. You will need to decide how much information you want to include on your tree and what you will do about missing names and duplicates.

Adding Branches

You might want to include additional branches of the family to your tree to show siblings or cousins. You might need to add in multiple marriages or other relationships. Calculating the number of people in the top generation could still help you to work out how much paper you need, but remember to allow extra space around each person so you can add more branches or other details.

Blank Spaces

You will probably also have some blank spaces in your tree. You might not know the names of all your relatives in all the generations you’re including on the tree. You’ll need to decide whether to leave a gap so you can fill in this information later (if you find it) or change the shape of the tree to make full use of the space you have.

Dealing with Doubles

Another common issue when drawing family trees is that we’re often connected to the same individuals through multiple lines. If two first cousins have a child, their shared grandparents will appear twice in that child’s family tree. Even if the parents were 6th or 20th cousins rather than first cousins, their family trees would still converge on those shared ancestors. You will need to decide whether these doubles (or multiples) should appear twice (or more) in your tree or if they can be named once and connected to multiple children.

The best approach for dealing with doubles on family trees can depend on how closely they are positioned. In the pictures above, the doubles are right next to each other so it is easy to remove one copy and connect them to both children. It can be trickier if their children are in different generations, placed far apart on the tree, or if only one person is duplicated because they had children with different partners. The tree can become tangled and harder to read.

Keeping duplicates on the tree can make it easier to draw as it’s more predictable. The parent-child relationships can also be clearer. However, unless you add something to show which people are duplicated, it would be easy to miss other relationships. If the people in the trees above weren’t coloured in then the first cousins and siblings wouldn’t be obvious. One option if you are using ahnentafel ID numbers would be to include all the numbers associated with duplicates whenever their names appear in the tree. This would show where else in the tree they can be found.

If you’re planning to draw your family tree and you want to include any additional branches or connections then it might help to use post-its or a pinboard to try different arrangements. There are also different styles and shapes of family tree that you could use.