Consanguinity Explained: Degrees of Blood Relation (Chart)

Consanguinity simply means being related by blood — descending from a common ancestor. The degree of consanguinity is a number that measures how close that blood tie is: your parent is a first-degree relative, your sibling is second degree, your aunt is third degree, and your first cousin is fourth degree under the most common counting system.

That's the short version. The longer version — how the counting actually works, why lawyers and priests historically used two different systems, and where these numbers still matter today — is what this guide covers. And if you'd rather skip the counting entirely, the free family relationship calculator on our homepage names any relationship (and its closeness) in a couple of clicks.

What Consanguinity Actually Means

The word comes from Latin: con (with, shared) + sanguis (blood). Two people are consanguineous if they descend from at least one common ancestor. Your siblings, parents, cousins, and great-grandparents all qualify. Your spouse, your in-laws, and your step-relatives don't — those are relatives by affinity (marriage), not blood.

Genealogists, lawyers, geneticists, and religious authorities have all needed a way to say how related two people are, not just whether they're related. The answer is the degree of consanguinity: a single number, where smaller means closer.

One important thing up front: there are two historical counting systems, and they give different numbers for the same pair of people. Most modern legal codes (and most charts you'll find online) use the civil law method, so that's the one this guide leads with.

How to Count Degrees of Consanguinity (Civil Law Method)

The civil law method is beautifully simple: count every parent–child step along the path connecting two people, going up to the common ancestor and back down. Each step is one degree.

Three worked examples:

1. You and your sibling. Up one step to your shared parents, down one step to your sibling. 1 + 1 = second degree.
2. You and your aunt. Up two steps to your grandparents (her parents), down one step to her. 2 + 1 = third degree.
3. You and your first cousin. Up two steps to your shared grandparents, down two steps to your cousin. 2 + 2 = fourth degree.

For direct ancestors and descendants there's no "down" leg — you just count the steps in the line. Parent = 1, grandparent = 2, great-grandparent = 3, and your own child = 1, grandchild = 2, and so on.

If you know cousin math already, the two systems connect neatly. Cousin degree is the shorter path to the common ancestor minus one, and "removed" counts the generation gap — our degrees of cousinship guide covers that. Civil-law consanguinity just adds both legs of the path together instead.

Consanguinity Chart: Degrees for Common Relatives

Here's the full chart for the relatives people actually ask about, with average shared DNA for context:

Notice something the chart makes obvious: the same degree can cover very different-feeling relationships. Your grandmother and your brother are both second-degree relatives. Your first cousin and your great-aunt are both fourth degree. The degree measures path length through the tree, not emotional closeness or even generation.

Also notice that shared DNA roughly halves with each added degree. That's not a coincidence — every parent–child step passes on about half of the relevant DNA, so each step in the path cuts the expected overlap in half.

The Canon Law Method (And Why Two Systems Exist)

Medieval church courts needed degrees too — mainly to enforce marriage prohibitions — and they counted differently. The canon law method counts only the longer leg of the path: the number of generations from the more distant person up to the common ancestor.

Under canon law:

• Siblings are first degree (each is one generation from the shared parents).
• First cousins are second degree (two generations from shared grandparents).
• A first cousin once removed is third degree (the longer leg is three generations).
• Second cousins are third degree as well.

This is why old records can look confusing. When a historical document says a couple needed a dispensation to marry "within the fourth degree," that's canon counting — it means they were third cousins or closer, which under civil counting would be eighth degree. If you do genealogy in European church records, expect the canon system; if you're reading a modern statute, expect civil.

There's also a third variant worth a sentence: some U.S. states historically used the "civil law" count as described here, while a few used collateral-degree tables of their own. The takeaway is always the same — check which system a document uses before you interpret its numbers.

Where Degrees of Consanguinity Matter Today

This isn't just trivia. The degree number does real work in several corners of modern life:

• Inheritance without a will. Intestate succession statutes distribute an estate to the closest relatives by degree, in a defined order. Understanding degrees is understanding who inherits — closely related to the rules covered in our next of kin guide.
• Marriage law. Every U.S. state bars marriage between close blood relatives; where they draw the line varies, and the line is expressed in relationships that map to degrees. First cousins (fourth degree) are the boundary case — see cousin marriage laws for the state-by-state picture.
• Medical and genetic screening. Doctors ask about first-degree and second-degree relatives when assessing hereditary risk, because shared DNA drops predictably with each degree. A condition in a first-degree relative means more, statistically, than the same condition in a fourth-degree one.
• Courts and conflicts of interest. Judges, jurors, and officials are commonly disqualified from matters involving relatives "within the third degree" (or similar wording). The degree is the test.
• Immigration and benefits rules. Various programs define eligible "family members" by enumerating relationships, which trace back to degree logic.

Consanguinity vs Affinity: Blood vs Marriage

Two people can be close family without any consanguinity at all. Affinity is the legal term for relation by marriage: your spouse, your parents-in-law, your stepchildren, your brother-in-law. Affinity has its own degree system in some legal codes (your spouse's second-degree relative is your second-degree affine), but no DNA is shared and no common ancestor exists.

A few practical consequences:

• Step-relatives and in-laws generally don't inherit under intestacy statutes — no consanguinity, no default claim.
• Adoption is the big exception to the "blood" framing: adopted children are treated as full first-degree relatives of their adoptive parents in modern law, with the same inheritance rights as biological children. The law deliberately creates legal consanguinity where genetic consanguinity doesn't exist.
• Half-relatives count, at reduced genetic overlap: a half-sibling is still a second-degree relative in most legal counts, though a few inheritance statutes treat half-blood differently. Whether the degree changes varies by jurisdiction; the DNA is half (about 25% instead of 50%).

The blood-versus-marriage distinction runs through the whole family tree — our guide to lineal vs collateral relatives breaks down the other axis lawyers care about: whether a blood relative is in your direct line or off to the side.

How to Work Out Any Degree Yourself

The full method, in four steps:

1. Find the nearest common ancestor (or ancestral couple) between the two people.
2. Count the parent–child steps from person A up to that ancestor.
3. Count the steps from the ancestor down to person B.
4. Add the two legs. That sum is the civil-law degree.

Two tips that prevent most mistakes. First, always use the nearest common ancestor — going back further inflates the count. Second, don't count the common ancestor themselves as a step; count the links, not the people.

If the path is tangled — half-relations, multiple marriages, "my grandma's cousin's daughter" territory — do yourself a favor and let the relationship calculator trace it. You pick how each person connects to the shared ancestor, and it returns the exact relationship name instantly, no scratch paper involved.

FAQ

What does consanguinity mean in simple terms?

It means blood relationship — two people who descend from a common ancestor. The degree of consanguinity is a number measuring how close that relationship is: parents are first degree, siblings and grandparents second, aunts and uncles third, first cousins fourth.

What degree of consanguinity is a first cousin?

Fourth degree under the civil law method used by most modern statutes: two steps up to your shared grandparents plus two steps down to your cousin. Under the older canon law method, first cousins are second degree.

Is a spouse a consanguineous relative?

No. Spouses are related by affinity (marriage), not consanguinity (blood). The same goes for in-laws and step-relatives. Adopted children are the special case: legally they're treated as full blood-equivalent relatives of their adoptive family.

What is the difference between the civil and canon law methods?

Civil law counts every step in the path — up to the common ancestor and back down — so first cousins are fourth degree. Canon law counts only the longer leg, so first cousins are second degree. Modern statutes almost always use the civil count; historical church records use canon.

Why do degrees of consanguinity matter legally?

They determine who inherits when someone dies without a will, which marriages a state permits, when a judge or juror must step aside, and which relatives count for various benefits. Medically, degree predicts shared DNA, which matters for hereditary risk assessment.

Are half-siblings the same degree as full siblings?

In most legal counting, yes — a half-sibling is still a second-degree relative, because the path through the one shared parent is the same length. Genetically they share about 25% DNA instead of a full sibling's 50%, and a minority of inheritance statutes give half-blood relatives a reduced share.

Put a Number on Any Relationship

Consanguinity sounds like a law-school word, but the idea is friendly: count the steps through the family tree, and you get a number that courts, doctors, and genealogists all understand. Parent, one. Sibling, two. Cousin, four. Everything else follows the same path-counting logic.

And when the path stops being obvious — someone at the reunion says "we're related through your great-grandma's sister" — don't count on your fingers. The free family relationship calculator traces the path, names the relationship, and settles it before the potato salad runs out.