Second cousins, cousins once removed; relationships by generations to common ancestor


Raymond Chen explains some common terms for blood relatives of varying distance across cultures in his blog post “What kind of uncle am I?

He links to a diagram on genealogy.com that I felt was lacking something… so here’s my version, with consanguinary colors.

Red means “marriage is almost certainly legally prohibited.”

Yellow means “marriage may be legally prohibited – check your region’s laws.”

Green means “marriage is amost certainly legal.”


Relationship by generations to common ancestor
# 0 1 2 3 4 m
0 self father/mother grand
(father/mother)
great‑
grand
(father/mother)
(great‑)2
grand
(father/mother)

(great-)m ‑ 2
grand
(father/mother)
1 son/daughter brother/sister aunt/uncle grand
(aunt/uncle)
great‑
grand
(aunt/uncle)

(great‑)m ‑ 3
grand
(aunt/uncle)
2 grand
(son/daughter)
niece/nephew (first) cousin first cousin,
once removed
first cousin,
twice removed

first cousin,
(m ‑ 2) times removed
3 great‑
grand
(son/daughter)
grand
(niece/nephew)
first cousin,
once removed
second cousin second cousin,
once removed

second cousin,
(m ‑ 3) times removed
4 (great‑)2
grand
(son/daughter)
great-
grand
(niece/nephew)
first cousin,
twice removed
second cousin,
once removed
third cousin
third cousin,
(m ‑ 4) times removed
n (great‑)n ‑ 2
grand
(son/daughter)
(great‑)n ‑ 3
grand
(niece/nephew)
first cousin,
(n ‑ 2) times removed
second cousin,
(n ‑ 3) times removed
third cousin,
(n ‑ 4) times removed

(n == m) ?

((n ‑ 1)th cousin) :

((min(n, m) ‑ 1)th cousin, |n ‑ m| times removed)
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