Resize a Facebook Page cover
Create an 851×315 cover image, the sRGB JPG size Facebook lists for fast Page-cover loading. Facebook’s cover guidance also notes that the image may be cropped and resized across screens.
Use JPEG for a photographic cover. PNG can keep hard logo edges sharper, but it may create a larger file.
Plan for responsive cropping
The initial resize uses a centered cover crop. Facebook can then apply another crop according to the device and Page layout. Keep names, dates, logos, and calls to action away from the top, bottom, and far-left edges.
The Page profile image can cover part of the left side. Preview the result inside Facebook before treating the composition as final.
Pixel size and file size
An 851×315 output is not automatically under Facebook’s fast-loading file-size recommendation. If the JPG remains above the desired limit, compress it after resizing and compare the text and logo edges before upload.