Black Pearls of Genealogy
Genealogy Labels
Shared CM Ranges For Relationships
| Relationship | Shared cM Range | Relationship | Shared cM Range | |
| Identical twins / Parent-Child | 3400 | Second Cousins / First Cousins Twice Removed / Half First Cousin Once Removed | 212.5 - 340 | |
| Full Siblings | 2300 - 2550 | First Cousins Once Removed / Half First Cousins | 170 - 212.5 | |
| Grandparent/Grandchild / Half-Siblings / Aunt/Uncle-Niece/Nephew | 1300 - 2300 | Second Cousins Once Removed / Half Second Cousins / First Cousins Twice Removed / Half First Cousins Once Removed | 106.25 - 170 | |
| Double First Cousins | 1200 - 1593.75 | Second Cousins Once Removed / Half Second Cousins | 85 - 106.25 | |
| First Cousins, Half-Aunt/Uncle, Half- | 850 - 1200 | Third Cousins / Second Cousins Twice Removed | 53.13 - 106.25 | |
| First Cousins / Great-Grandparent/Great-Grandchild | 680 - 850 | Third Cousins Once Removed | 26.56 - 53.13 | |
| First Cousins, Half-Aunt/Uncle, Half-Niece/Nephew | 425 - 680 | Fourth Cousins / Third Cousins Twice Removed | 13.28 - 26.56 | |
| First Cousins Once Removed / Half First Cousins | 340 - 425 | Fourth Cousins Once Removed / Third Cousins Three Times Removed | 6.64 - 13.28 | |
| Double Second Cousins | 340 - 425 | Fifth Cousins | 3.32 - 6.64 | |
Why should I Use 7cM as your default?
The 7 cM threshold is commonly used in genetic genealogy platforms like AncestryDNA, 23andMe, and MyHeritage as a default setting for viewing DNA matches because:
To Reduce False Matches:
- Small segments (typically below 7 cM) are more likely to be identical by state (IBS) rather than identical by descent (IBD).
- IBS segments can appear due to coincidental recombination rather than true shared ancestry.
Increases Confidence in Matches:
- At 7 cM or higher, the probability of a real genealogical relationship increases.
- Many companies have even raised their minimum threshold over time (e.g., AncestryDNA now excludes matches under 8 cM unless they meet additional criteria).
Prevents Overload of Distant Matches:
- If the threshold were too low, people would have thousands of distant matches, many of which are not useful for genealogy.
- A 7 cM setting ensures that you focus on closer and more reliable connections.
Note: This is ultimately a personal preference. You may choose to lower the cM threshold below 7 cM if you’re specifically searching for more distant connections. However, be mindful that smaller segments have a higher likelihood of being false matches.
