You may have noticed recently that your Facebook header cover is cut off on the sides when your page is viewed on a mobile device and be saying to yourself, “but I created it in the recommended 828 x 315 pixel size.”
The reason: Facebook changed the display size for mobile last year so the trick is to make your header cover image much taller than the recommended 828 x 315 pixels.
To get everything to display in the proper aspect ratio, create an 828 x 464 pixel file with the understanding that 75 pixels on the top and bottom will be cropped off when viewed on a desktop (so keep what is in those areas benign). Also, know that Facebook no longer overlays the profile image in the lower left-hand corner (it’s displayed on a sidebar now), so use that area for content if applicable.
Finally, remember to upload your file as a PNG file for better resolution by avoiding image compression.