Can. 108 §1. Consanguinity is computed through lines and degrees.
§2. In the direct line there are as many degrees as there are generations or persons, not counting the common ancestor.
§3. In the collateral line there are as many degrees as there are persons in both the lines together, not counting the common ancestor.
Can. 109 §1. Affinity arises from a valid marriage, even if not consummated, and exists between a man and the blood relatives of the woman and between the woman and the blood relatives of the man.
§2. It is so computed that those who are blood relatives of the man are related in the same line and degree by affinity to the woman, and vice versa.
Can. 1091 §1. In the direct line of consanguinity marriage is invalid between all ancestors and descendants, both legitimate and natural.
§2. In the collateral line marriage is invalid up to and including the fourth degree.
§3. The impediment of consanguinity is not multiplied.
§4. A marriage is never permitted if doubt exists whether the partners are related by consanguinity in any degree of the direct line or in the second degree of the collateral line.
Can. 1092 Affinity in the direct line in any degree invalidates a marriage.