How are you related?

Every blood relationship comes down to two numbers. Count how many generations you go up from you to the nearest shared ancestor, and how many generations down from that ancestor to the other person. Kinage calls these a and b. The pair fixes the name.

The smaller number, minus one, is the cousin degree. The gap between the two is the number of times removed. If one of you is the ancestor of the other, there is no cousin at all: the relation is a straight line, such as grandparent or great-niece.

Half relatives share just one ancestor rather than a couple. Kinage spots this from the route you give it, and says so. Step, foster and in-law links are named too, but they are by marriage or care, so no shared DNA is expected.

Take the route shown above: your mother's mother's mother, then her daughter, then that daughter's son. You go up three steps to your great-grandmother, so a = 3. From her you go down to her daughter, then to that daughter's son: two steps, so b = 2.

The cousin degree is the smaller number, 2, minus one: first cousin. The numbers differ by one, so the removal is one. Your relative is your first cousin once removed. Read the full explanation of this term.

Not sure of the counting? The relationship chart lays out every pair of a and b from 1 to 8, and the guide to cousin degree and removal walks through the rule step by step.

• All 65 relationship terms, from child to eighth cousin, with their reciprocals and DNA averages.
• Build a family tree that stays on your device, and ask how any two people on it are related.
• The cousin chart, an interactive grid of every common relationship.
• Guides on half relatives, in-laws, marriage law, GEDCOM files and DNA.