TINYTEXT, TEXT, MEDIUMTEXT, and LONGTEXT maximum storage sizes

From the documentation (MySQL 8) :

      Type | Maximum length
-----------+-------------------------------------
  TINYTEXT |           255 (2 8−1) bytes
      TEXT |        65,535 (216−1) bytes = 64 KiB
MEDIUMTEXT |    16,777,215 (224−1) bytes = 16 MiB
  LONGTEXT | 4,294,967,295 (232−1) bytes =  4 GiB

Note that the number of characters that can be stored in your column will depend on the character encoding.