Text Limiter is an extension for Meta Box plugin which allows you to limit number of characters or words entered for text, textarea and WYSIWYG fields.
To start using text limiter, just add the following parameters to text, textarea, or wysiwyg fields:
'limit' => 20, // Number of characters or words
'limit_type' => 'character', // Limit by 'character' or 'word'. Optional. Default is 'character'