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Centimorgan Relationship Calculator
Updated on November 4, 2022
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Centimorgan Relationship Calculator
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A centimorgan relationship calculator predicts how closely related you are to someone. The more centimorgans you have in common, the closer your relationship.

Genetic testing companies use centimorgans to find common ancestors you share with a particular group of people. It helps them estimate your ethnicity.

Centimorgans can also help DNA companies find people you’re related to.

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What Is A Centimorgan?

Our DNA comes from the chromosomes we inherited from our parents. This is why we share segments of the same genetic material with our parents and biological family.1

A DNA segment refers to the position in a chromosome where a DNA match starts and ends. You and your relative can have multiple shared segments.2

Geneticists use centimorgans (cM) to measure the length or size of DNA segments you share with other people. It is a unit that describes how much DNA you have in common.

You’re likely to share more DNA segments or cM counts with close family members. But you might have a lower cM count with distant relatives. 

How Many Centimorgans Does A Person Have?

Each person has about 6,800 centimorgans. A centimorgan relationship calculator measures how much out of the 6,800 cM you share with someone else.

However, DNA testing companies may count fewer centimorgans.3

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How To Calculate Your Shared DNA Using Centimorgans

The cM calculator shows the percentage of DNA you have in common with a person. Knowing how many centimorgans you share can tell you how closely related you are. 

You can calculate the total percentage of shared DNA with this formula:

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If you share 1,800 cM with a family member, here’s what it would look like:

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What Is A Centimorgan Chart?

A centimorgan chart estimates your relationship with people based on the amount of shared cM. Blaine Bettinger, a genealogy expert, developed the system in 2016.

Years of study led Bettinger to creating the shared cM project. Currently, it’s in its third version. 

His ongoing research helps genealogists predict possible genetic connections between people with matching DNA segments.

How to Use A Centimorgan Chart

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First, you need to know the total cM shared with a genetic match. The next step is to look it up on the Bettinger DNA cM chart and do the following:

  1. Look at the Cluster Chart and compare your total number of shared centimorgans with the ranges indicated in the 95th percentile. Take note which clusters your cM falls into.
  2. On the Cluster Chart, compare your total shared cM with the average and see which clusters it is closest to. Take note which clusters your cMs best fit into.
  3. Using your results from step 2, review the Histogram. See which relationships the total shared cM is nearest the peak of the histogram.

Source: The Shared cM Project, The Genetic Genealogist

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Step 1 can help you identify all possible relationships with a genetic match. Steps 2 and 3 help you narrow down your most likely relationships with a person.

Using Centimorgans To Find Relatives

DNA companies like Ancestry DNA and 23andMe can help you find potential relatives. Many of these services use centimorgans to estimate your relationship with a DNA match.

For instance, they can tell if your DNA match is a potential cousin or aunt.

You can take the test yourself. But you can also ask living family members to take DNA tests from the same company. 

This allows you to explore more genetic matches and improve the accuracy of results. However, further DNA testing is needed to determine your biological connection.

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Resources

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  1. Heredity, Genes, and DNA.” The Cell: A Molecular Approach.
  2. What is a segment?” Segmentology.
  3. Autosomal DNA statistics.” International Society of Genetic Genealogy Wiki.
  4. August 2017 Update to the Shared cM Project.” The Genetic Genealogist.
Cristine Santander
Cristine Santander
Content Contributor
Cristine Santander is a content writer for KnowYourDNA. She has a B.S. in Psychology and enjoys writing about health and wellness.
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