The maximum lengths of the subject and message body can be configured in the standard Gerrit config file gerrit.config. The defaults are 50 characters for the summary and 72 characters for the description, as recommended by the git tutorial and expanded upon by Tim Pope.
commitmessage.maxSubjectLength : Maximum length of the commit message's subject line. Defaults to 50 if not specified or less than 0.
commitmessage.maxLineLength : Maximum length of a line in the commit message's body. Defaults to 72 if not specified or less than 0.
commitmessage.longLinesThreshold : Percentage of commit message lines allowed to exceed the maximum length before a warning or error is generated. Defaults to 33 if not specified or less than 0.
commitmessage.rejectTooLong : If set to true, reject commits whose subject or line length exceeds the maximum allowed length. If not specified, defaults to false.