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.
Meta Box Lite
We recommend using Meta Box Lite, a feature-rich free UI version of Meta Box that provides UI and all free features for managing custom fields and dynamic content on WordPress, including post types, taxonomies, custom fields, and relationships.
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'