Centimorgan DNA Relationship Calculator
Enter your shared DNA details to instantly predict your potential relationship with a DNA match.
Enter Shared DNA
Common Relationship Presets
No standard matching genetic relationships found for this cM value.
Pedigree Highlight Mapper
(~1750 cM)
(~3400 cM)
(~1750 cM)
(~2550 cM)
(~875 cM)
(~1750 cM)
(~230 cM)
Note: Tree highlights the closest standard relationship tier matching your input DNA values.
Understanding Genetic Distance & Centimorgans
What is a Centimorgan (cM)?
A centimorgan (abbreviated as **cM**) is a unit of genetic measurement. Named after pioneer geneticist **Thomas Hunt Morgan**, it does not measure physical length on a chromosome, but rather the likelihood of crossover happening during genetic meiosis (cell replication).
Specifically, 1 centimorgan corresponds to a **1% probability** that a specific segment of DNA will separate or recombine in a single generation.
How is DNA Percentage Converted?
A person inherits 50% of their DNA from their mother and 50% from their father. In total, a single set of chromosomes contains roughly **3,400 centimorgans** of DNA (measured by genetic matching firms).
We calculate percentage using the formula:
Shared % = (cM / 3400) * 100
Using this model, sharing 870 cMs equates to roughly 25.5% shared DNA, typical of a grandparent or half-sibling relation.
Crucial Factors: Pedigree Collapse & Endogamy
While centimorgan calculations provide mathematical estimates, human genealogy can be complex:
- Overlapping Ranges: Because genetic crossovers are randomized, a full sibling can share anywhere from 2200 cM to 3100 cM. The same value (e.g. 1750 cM) can indicate a grandparent, half-sibling, or uncle.
- Pedigree Collapse: Happens when ancestors marry cousins, reducing the size of the unique ancestral tree. This can cause you to share more DNA with a relative than standard tables predict.
- Endogamy: Common in isolated populations (like Ashkenazi Jewish, Island populations, or Amish groups) where members married within the community for centuries. This results in matches sharing a high density of small, identical DNA segments, inflating the estimated relationship closeness.