This page provides a brief educational overview of how AncestryDNA estimates family relationships using shared DNA measured in centimorgans (cM). It may be helpful for individuals reviewing DNA matches and trying to understand possible relationships such as close family members, cousins, or more distant relatives.
DNA Shared Centimorgan Ranges (approximate)
AncestryDNA compares the amount of shared DNA between two individuals to estimate likely relationships. These ranges are approximate and may vary:
- ~3,400–3,800 cM: Parent / Child or identical twin
- ~2,300–2,900 cM: Full siblings
- ~1,300–2,300 cM: Grandparent, aunt/uncle, niece/nephew, half-sibling
- ~680–1,300 cM: First cousins / great-grandparent level relationships
- ~200–600 cM: Second cousins
- ~90–180 cM: Third cousins
These estimates can help narrow down possible relationships, especially when combined with traditional genealogy research.
Example Personal Matches
In my own AncestryDNA results, I have observed shared DNA amounts such as:
- 829 cM and 872 cM with known first cousin matches
- 1,550–1,975 cM with niece/nephew-level matches
These comparisons help confirm or clarify relationships that may not be immediately obvious through family records alone.
Ethnicity Estimates (Example)
AncestryDNA also provides ethnicity estimates based on genetic markers. My results include:
- Ireland / Scotland / Wales: 37%
- Great Britain: 21%
- Europe West: 21%
- Scandinavia: 17%
- Smaller percentages: Southern Europe, Eastern Europe, Iberian Peninsula (<1–2%)
Ethnicity estimates are updated periodically as reference data improves.
Originally posted on the Davenport Family Facebook Group on 04/22/18