Here are the recommended Facebook image sizes (in pixels) for various purposes:
Facebook profile photo or page logo: 180×180 (at least this size square, .png looks best for this)
Cover image: 851w x 315 h (.jpg)
Image in a post: 1200w x 900h, larger images will be truncated. The minimum size of 560w x 292h is unique in that it can work on Facebook, Twitter, LinkedIn and Google+.
More information can be found at: https://www.facebook.com/help/125379114252045
For webmasters: The Open Graph image size is 1200w x 628h.
For more information about adding Open Graph meta tags to your site, contact us.