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)