What Are Centimorgans (cM)?

One of the first things you'll notice when viewing your DNA matches is a number followed by the letters cM.

But what exactly does it mean?

A centimorgan (cM) is a unit used to estimate how much DNA two people share.

The more centimorgans you share with another person, the more closely you're generally related.

For example:

• Parent/Child — approximately 3,400 cM
• Full Siblings — approximately 2,300–3,700 cM
• First Cousins — approximately 575–1,330 cM
• Second Cousins — approximately 75–360 cM

It's important to remember that these are ranges—not exact values.

Because DNA is inherited randomly, two people with the same genealogical relationship may share different amounts of DNA.

This is why genealogists combine DNA evidence with traditional records such as birth certificates, census records, probate files, and other historical documents.

Centimorgans help us narrow down possible relationships, but they are only one piece of the puzzle.

Understanding cM values is one of the first and most important steps toward making sense of your DNA matches and discovering how you fit into your family's story.

🌳 Lineage By Laura
Where Family History Meets Identity Discovery