The number every match list shows you, and almost nobody explains
Open your match list on AncestryDNA, 23andMe, MyHeritage or FamilyTreeDNA and the first thing you see next to every name is a number in "cM", centimorgans. Most sites never explain what that number actually means, so people either ignore it or assume it maps to exactly one relationship. Neither is quite right, and the gap between "here is a number" and "here is what it tells you" is exactly what trips people up.
What is a centimorgan?
A centimorgan is a unit of genetic distance, not physical distance. It measures how likely a stretch of DNA is to be broken up by recombination when passed from parent to child. In practice, for a match list, all that matters is this: the more centimorgans (cM) you share with someone, the more DNA you have in common, and the more closely related you probably are.
Quick reference: shared cM by relationship
These are the standard, widely-published Shared cM Project ranges. Real matches vary within these ranges, sometimes considerably, but the average is your best single guess when you have nothing else to go on. The scale below is logarithmic, since relationships span three orders of magnitude, from a parent/child pair sharing over 3,000 cM down to a distant cousin sharing barely 20.
Average shared cM per relationship tier, with the full published range. Ranges overlap heavily between adjacent tiers, which is exactly why the same cM number can point to more than one relationship.
Want to look up your exact number instead of reading a chart? → Try the interactive cM → Relationship Chart, paste your cM (or percentage) and it ranks the likely relationships for you.
And if you have two raw DNA files on hand (yours and a relative's), our free One-to-One Kit Comparer goes one step further: it measures the DNA you actually share, segment by segment in centimorgans, and estimates the relationship directly, 100% in your browser, no upload to any server.
Why the same cM number can point to different relationships
Here is the part that confuses people the most: a single cM number does not map to a single relationship. Someone sharing around 1,700 cM with you could be a grandparent, an aunt or uncle, a half-sibling, or a double first cousin, because random recombination means the exact amount of DNA passed down varies from one family relationship to the next, and different relationships overlap in range, as the chart above shows. The number tells you the likely tier, not the exact relationship, other clues (age, shared family names, which side of the family, X-DNA) narrow it down from there.
Where to find your cM number on each site
| Site | Where the number is shown |
|---|---|
| AncestryDNA | Directly under the match's name, as "X cM across Y segments" |
| 23andMe | "% DNA shared" on the match card, cM shown on the relative's detail page |
| MyHeritage | Both a percentage and a cM total under "Shared DNA" on the match page |
| FamilyTreeDNA | "Shared cM" and "Longest Block" in the Family Finder match list |
Why your real number rarely matches the chart exactly
Recombination is random, so no two siblings inherit exactly the same amount of DNA from a shared ancestor, and the published ranges reflect that real-world spread rather than a single fixed value. A first cousin averaging around 870 cM can genuinely land anywhere from roughly 400 to almost 1,400 cM and still be a completely ordinary first cousin. If your number falls between two tiers, both are worth considering until other evidence (family trees, shared matches, which parent's side) narrows it down.
Beyond who you match, where they came from
A match list tells you who you are related to. It does not tell you where your own ancestors actually came from, that is a different kind of DNA analysis entirely (autosomal admixture modelling against ancient and modern reference populations, not match segments). If that is the question you are actually trying to answer, our Advanced Ancestry Report compares your DNA against over 2,000 modern reference populations worldwide, or browse our 14 region-specific Focus reports if you already know roughly where your family is from.