The standard character limit for a tweet is 280 characters. Twitter doubled the original 140-character limit in November 2017, initially applying the change to most languages while retaining special treatment for Chinese, Japanese, and Korean. The expansion was intended to reduce the need for users to compress their thoughts unnaturally.
The original limit came from Twitter’s mobile-phone roots. Early Twitter messages were designed around the 160-character limit of SMS text messages, with space reserved for a username. The company settled on 140 characters as a practical, uniform limit, helping give the service its famously concise style.
Many people still answer 140 because that limit defined Twitter for its first decade. The number 280 is the standard limit for ordinary posts, although some paid X subscriptions have offered much longer posts. That extended feature does not change the conventional answer for a standard tweet. Links, usernames, and attached media are also handled differently from ordinary typed characters in the composer.