Board Thread:Support Requests - Designing Your Wikia/@comment-24300478-20140403091901/@comment-168424-20140404001644

A wordmark should be a 250 pixel wide by 65 pixel tall (250x65) PNG (.png aka Portable Network Graphic).

Here's some info on how to upload the wordmark to your wiki once you've made it: How to upload a logo to your wiki.