Shared cM by relationship.

Worked example

A match shares 850 cM, which is 850 ÷ 7,440 = 11.4%. Nine relationships have a published range that includes 850 cM. The closest averages are great-aunt or uncle and great-niece or nephew (average 850), first cousin (866), half aunt or uncle (871) and great-grandparent (887). Half first cousin (449) and first cousin once removed (433) also fit because their ranges reach 979 and 980. A match this size could be many of these, so use tree and age evidence to decide.

How it works

The table is the Shared cM Project 4.0 data by Blaine Bettinger (interactive version at DNA Painter, last updated 26 March 2020). Each row is an average and a low to high range of the total centimorgans shared across 56 relationships, compiled from results people submitted. A centimorgan is a unit for measuring genetic linkage, defined by the expected average number of crossovers in a single generation being 0.01.

Matching lists every relationship whose range contains your number, ordered by how close your number is to that relationship’s average. That ordering is not a probability. The source tool warns that for relationships more distant than half second cousin the averages come only from cases where DNA was shared, that the more distant the relationship the more likely two people share no DNA at all, and that the statistics do not allow for pedigree collapse or endogamy. Different testing companies report different totals, so a percentage from one company can differ from the percentage here.

Sources and basis (opened 2026-10-08): DNA Painter, Shared cM Project 4.0 tool v4 (last updated 26 March 2020) (averages, ranges, the 7,440 cM total and the cautions above); Centimorgan - Wikipedia (definition).

FAQ

How many cM do first cousins share?

In the Shared cM Project 4.0 data the average for first cousins is 866 cM, with a range of 396 to 1,397 cM.

How many cM do second cousins share?

The average for second cousins is 229 cM, with a range of 41 to 592 cM.

How many cM does a half sibling share?

The average for half siblings is 1,759 cM, with a range of 1,160 to 2,436 cM. Full siblings average 2,613 cM with a range of 1,613 to 3,488 cM.

What is a centimorgan?

A centimorgan (cM) is a unit for measuring genetic linkage. It is the distance between two positions on a chromosome where the expected average number of crossovers in a single generation is 0.01. DNA tests report shared DNA in cM.

Can a distant cousin share no DNA at all?

Yes. In this data the ranges for third cousins and more distant relatives start at 0 cM, and the source tool notes that the more distant a relationship, the more likely two people are related but share no DNA.

Why does one cM amount fit many relationships?

The ranges overlap. A single amount of shared DNA can fit several relationships, so the tool lists every relationship whose range includes it rather than naming one.