on the dna centimorgan measurement system that they use. The more centimorgans you share with someone , the closer they are related to you. There is a standard deviation/fluctuation where a full sibling may share much more cMs with you than another sibling does but full siblings will be within a given range of deviation.

In the first image here, I have a half sibling that shows up in ancestry.com’s “close family” category. This half sibling in here is next to an uncle and aunt of mine. Considering my half sibling and I share dna from one parent, it makes sense that this sibling shows the same level of relation as an aunt or uncle.

In the next image I have two aunts and one uncle who are my “half aunt/uncles”. One aunt is my moms half sister, and the other aunt and uncle are my dads half sister and half brother.

My “half” aunts and uncles show up in the 1st cousin category which makes sense considering we share DNA from one of their parents. With me being a generation removed, I would share a quarter of my DNA with them like we do with a typical 1st cousin.

We always knew about one aunt and one uncle, with both of them raised by my grandmothers and essentially adopted by my grandfathers in each case. In the other case of the “half aunt”, this was discovered through ancestry.com. She reached out to me excited about finding her new “1st cousin”. When I learned she was roughly 40 years older than me and began connecting the dots, it became clear she was my paternal grandfathers biological daughter. Especially how she matched up with my dad and his siblings the exact same way their known half brother did already.

Again, if this is from ancestry.com then you’ll want to look at the centimorgans (cM) listed with your matched relatives and from there you can connect dots pretty easily when comparing against known relatives and relation.