Does anyone know if possible to set like 80 characters per row in TinyMCE?
There's no out of the box functionality to acheive this. What are you trying to accomplish?
@Katharina, it would be also worth telling at least which TinyMCE (EPiServer.CMS.TinyMce) NuGet package version you are using 1.x or 2.x as the 2.x package introduced the new TinyMCE v4 editor (so that people can suggest solution for correct TinyMCE version).
Anikets question about what are you trying to accomplish is very valid.
The content on the "row" can contain HTML tags, so are you counting the content that includes the HTML also or just the "visible" characters (can produce interesting results for the user if HTML tags are also counted, user pastes 80 characters and then applies formatting and oops it is more than 80 characters).
Thanks Antti and Aniket. I think I'll try to adjust with width in css instead. See if it look better.