Ranges overlap, so this is a rough guide based on Shared cM Project averages. Not a medical result.
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The centimorgan chart.
Average shared DNA by relationship, with the range most real pairs fall into. Notice how much the ranges overlap: 400 cM could be a first cousin or a second cousin.
| Relationship | Average shared cM | Typical range | Marry in the US? |
|---|---|---|---|
| Parent / child | 3,485 | 2,376–3,720 | Illegal everywhere |
| Full sibling | 2,613 | 1,613–3,488 | Illegal everywhere |
| Half sibling | 1,759 | 1,160–2,436 | Illegal everywhere |
| Grandparent / grandchild | 1,754 | 984–2,462 | Illegal everywhere |
| Aunt / uncle, niece / nephew | 1,741 | 1,201–2,282 | Illegal everywhere |
| Great-grandparent | 887 | 485–1,486 | Illegal everywhere |
| Half aunt / uncle | 871 | 492–1,315 | Depends on the state |
| First cousin | 866 | 396–1,397 | Depends on the state |
| Great-aunt / uncle | 850 | 330–1,467 | Depends on the state |
| Half first cousin | 449 | 156–979 | Depends on the state |
| First cousin once removed | 433 | 102–980 | Depends on the state |
| Second cousin | 229 | 41–592 | Legal in all 50 states |
| First cousin twice removed | 221 | 33–471 | Legal in all 50 states |
| Second cousin once removed | 122 | 14–353 | Legal in all 50 states |
| Third cousin | 73 | 0–234 | Legal in all 50 states |
| Third cousin once removed | 48 | 0–192 | Legal in all 50 states |
| Fourth cousin | 35 | 0–139 | Legal in all 50 states |
| Fifth cousin | 25 | 0–117 | Legal in all 50 states |
Data: the Shared cM Project v4 by Blaine Bettinger (CC BY 4.0). Marriage column summarizes US state law for first-cousin and closer relationships. See cousin marriage laws.
Why your match list can't give you one answer
DNA is passed down in random chunks, so two first cousins might share 550 cM while another pair shares 1,200. That's why the ranges overlap, and why a half-sibling, a grandparent and an aunt can all show up at around 1,750 cM. How to tell full from half siblings.
Your testing company also only compares you with people who tested with the same company. If your partner tested with 23andMe and you tested with Ancestry, you'll never appear in each other's match lists, even if you're siblings.
That's what our check is for
Drop both raw DNA files into the free relatedness check, whichever company they came from, and it compares them directly in your browser. Nothing is uploaded. Haven't tested? Here's which kit to get.
Different companies? We compare them.
Ancestry vs. 23andMe vs. MyHeritage files can't see each other. We check them against each other, right in your browser. Free while in beta.
cM questions.
What is a centimorgan (cM)?
A centimorgan is a unit for measuring stretches of DNA. DNA testing companies add up the length of all the matching segments two people share, and the total in cM tells you roughly how closely related you are.
How many cM do siblings share?
Full siblings share about 2,613 cM on average (range roughly 1,613–3,488). Half siblings share about 1,759 cM.
How many cM do first cousins share?
First cousins share about 866 cM on average, with a typical range of 396 to 1,397 cM.
How many cM do second cousins share?
Second cousins share about 229 cM on average, anywhere from about 41 to 592 cM.
How many cM means you are not related?
Under about 20 cM is usually distant or noise from shared ancestry far back. Two strangers from the same population can share a few small segments without a genealogical link.
Where do I find my shared cM?
On AncestryDNA, open DNA Matches and click a match. On 23andMe, open DNA Relatives and the match profile. On MyHeritage, open DNA Matches and review the match. Each one shows the total shared cM.