On Facebook, the large banner image at the top of a personal profile or Facebook Page. Cover images are 851 pixels wide by 315 pixels tall.
Why are Cover Images important?
Your brand's cover image is the first thing Facebook fans see when they visit your Page. It is an opportunity to showcase your best products or share part of your brand's story with visitors. Using a high quality, engaging cover image is a great way to instantly capture the attention of fans and followers. See an example of a Facebook cover image below: