Computing blood line relationships

Consanguinity or computing blood line relationships

Consanguinity is the relationship between one person and another who each share a blood line.

We usually express this relationship as

  • great great grandmother (or great great grandfather)
  • grandmother (or father)
  • mother (or father)
  • brother (or sister)
  • aunt (or uncle)
  • cousin
  • first (etc) cousin

It may well carry a further expression “once (or twice etc) removed”

There is a Consanguinity Chart  in this site’s image albums (click on that linked title to open up the chart) which may assist in making sense of how this relationship classification works.


Lets assume that is someone in a hypothetical fictional family (lets call him Adam) has found a new addition for his tree (lets call him Joseph) to add to his tree.

If Joseph’s grandfather is Adam’s grandfather, what is the relationship between Joseph & Adam?

  • Assume Adam is is the box “subject” on the chart
  • look up and along to “box 3 Grandparents
  • now look down two generations and you will find that Adam and Joseph are “first cousins”

If Adam’s Grandfather is Joseph’s great grandfather then you would need to drop down three generations and in that case Joseph would be Adam’s first cousin once removed.

Hope that helps!!