Calculate relatedness

Is it possible to calculate the relatedness between family members(consanguineous) if you have the genotypes at all positions on te chromosomes.

Let me try to explain what I'm doing now:

A person can have 3 types of genotypes for example AA, BB and AB. If you combine 2 persons you will get a total of 9 different types of combinations.(AAAA,BBBB,ABAB,AAAB,BBAB,ABBB,ABAA,AABB and BBAA)

If you count all the AAAA,BBBB and ABAB and give them a number (2). I did this also for the AAAB,BBAB,ABBB,ABAA and give them the number 1. And the last two AABB,BBAA i give them number 0 because they are totally different.

(From here see attachment)
Count all the number 0,1,2 and this is the Identity by state.(IBS0,1,2)
Now you can calculate from persons in 1 family and individuals how related they are. (1.5 not related till 1.8 very close related)

Is there an other way to calculate the relatedness between 2 persons if you have the genotypes at all positions?