I was looking around for a short post that summarised the character limits on the various twitter fields, and I couldn’t find it anywhere, so I worked it out. Here it is for future reference:
Username: 15 characters
Full name: 20 characters
Location: 30 characters
URL: 100 characters
Bio: 160 characters
Tweet: 140 characters (obviously)
For a retweet, the popular wisdom is to limit yourself to 120 characters to allow room for the “RT @” and a separator.
Lists: no more than 20 per account
Did I miss anything?