By size you mean the amount of text for a given card? Like the number of characters displayed?
I don’t think there is a way to do that currently, but I might be wrong. Let’s see what other people say.
However, it could be a good suggestion for the Advanced Browser add-on. They say users can open an issue on Github to suggest new columns for the add-on.
Export to txt. Open in one of the spreadsheet programs (Google spreadsheets, excel, libreoffice). Use the function to count characters in a table cell.
I like @keks’s spreadsheet idea, but the other idea I had is to use regex (Searching - Anki Manual) to search you main field for any that have over X characters.
Keep in mind that whatever you choose, a card with formatting is always going to have more characters than a card without – because all of those HTML tags count. I suppose you could craft a regex search that ignores certain things, like characters between < > – but that pretty quickly gets pretty complicated with exclusions and inclusions.