I came into a eagle plate carrier and a MTV both in size medium. it looks like a size large plate will fit in them but I'm not sure if a large plate goes in a large carrier and a medium goes in the medium???
your vest is the same size as the plate it holds. the ESAPI plates get really big as you go up in size. if you have a medium carrier thats what will fit. In the army the size of my soldiers large IOTV is alot bigger no way a large would fit in my small vest
The Eagle plate carrier only comes in two sizes, S/M and L/XL, and they are sized to fit the corresponding mil-spec SAPI sized plates.
The common 10"x12" plate is a commercial size and does not match directly to a SAPI size. I have used 10x12 plates in both sizes of Eagle plate carriers.
Before you buy any plates, I suggest you make up some dummy plates out of cardboard. You can laminate the cardboard together to get the correct thickness and cut them to the desired dimensions.
Get the dimensions on any plates you are considering and mock them up. You can get a feel for how different sizes will work for you.