|The Aeron Chair comes in small, medium, and large sizes (A, B, and C). Click here for a full version of the size chart.|
The size chart is your guide to finding which size is right for you. If you fall into the B/C category and you have long legs, choose size C; you'll want the deeper seat. If you have short legs, go with a B, since the size C front seat edge will dig into the back of your calves (which will outweigh the benefit of the added 1.5" width you get with a size C).
Also, if you fall into the B/C category, have a long torso, and lean back a lot while sitting, the extra 3" you gain in the height of the back with a size C will benefit you.