🧬 cM → Relationship Chart
Got a DNA match on AncestryDNA, 23andMe, MyHeritage or FamilyTreeDNA showing a "shared cM" number and no idea what it means? Type it in below and find out who they probably are.
What is a centimorgan (cM)? A centimorgan is a unit of measurement for genetic linkage, basically a way to measure how much DNA two people have in common. The more DNA (measured in cM) you share with a match, the more closely related you probably are. Every DNA testing company (AncestryDNA, 23andMe, MyHeritage, FamilyTreeDNA, LivingDNA) shows this number next to each of your matches.
Why doesn't one cM number mean one relationship? Because inheritance is random. Both a grandparent and a half-sibling typically share around 1,750 cM with you, and both a first cousin and a half-aunt can land in overlapping ranges. That's why a single shared cM figure always maps to a range of possible relationships, not one guaranteed answer, family trees, ages, and shared surnames are what narrow it down from there.
Enter either the shared cM number or the % shared DNA, most sites show one or both next to a match. Total autosomal DNA is ~6,800 cM, so % × 68 ≈ cM.
Full Shared cM reference chart
These are the standard, widely published ranges popularized by the Shared cM Project (a crowdsourced dataset of real, tree-confirmed relationships). Ranges overlap on purpose, real DNA inheritance is noisy, so treat the average as your best single guess and the range as "still plausible."
| Relationship | Average shared cM | Typical range | % shared DNA (avg) |
|---|
How to read your DNA match list
Each testing company shows the shared cM number in a slightly different place:
🧬 AncestryDNA
Open a match, click "View match", then check under their name for something like "Shared DNA: 1,742 cM across 34 segments". Ancestry also assigns a relationship label (e.g. "Close Family"), which is its own estimate, not a guarantee.
🧬 23andMe
Under "DNA Relatives", click a match, then "Relatedness" or the match details panel shows "X% DNA shared, Y segments" (e.g. "12.7% shared"). Multiply the percentage by ~68 to estimate cM (23andMe reports segments in cM too if you expand the details).
🧬 MyHeritage
On the DNA Matches page, each match card shows a percentage and a "Shared DNA" figure directly, e.g. "3.4% shared, 245.3 cM across 12 segments". Click "Review DNA Match" for the full segment breakdown.
🧬 FamilyTreeDNA (FTDNA)
On the "Family Finder Matches" page, the "Shared cM" and "Longest Block" columns are shown directly in the match table, no extra clicks needed. FTDNA also shows an "X Degree Relative" range in the same row.
Frequently asked questions
Why does the same cM number map to different relationships?
DNA inheritance from each parent is random (recombination), so the exact amount two relatives share varies around an average instead of landing on one fixed number. A grandparent, an aunt/uncle, and a half-sibling all average around 1,750 cM and their ranges overlap heavily, so the cM number alone can't distinguish them; you need other clues like age, generation, and known family members in common.
What is a centimorgan (cM)?
A centimorgan is a unit of genetic distance, not physical distance, that measures how likely a DNA segment is to recombine (be split) between generations. In practice, "shared cM" is simply the total length of all the DNA segments you and a match have in common. Your full autosomal genome is about 6,800 cM, so a full sibling sharing ~2,600 cM shares roughly 38% of your DNA.
Why don't my results match a chart exactly?
Charts like this one show the observed range from thousands of real, tree-confirmed relationships (the Shared cM Project), not a mathematical guarantee. Endogamy (repeated intermarriage within a small population), half-relationships, and simple random chance can all push your number toward the edge, or even slightly outside, the typical range for your true relationship.
Is this tool free and does my data leave my browser?
Yes. This calculator runs entirely in your browser using a hardcoded reference table, the cM number you type is never sent anywhere or stored.
Can this chart tell me exactly how I'm related to a match?
No single cM number can give you a 100% certain answer beyond parent/child or full sibling ranges. Use this chart to narrow down the plausible relationships, then confirm with shared matches, family trees, and known relatives in common.