Facebook Web Link Image Size. While facebook has not recommended a size i tested and found that you can upload any size and choose your preferred cropping but it will be in this 1 91 1 aspect ratio. This thumbnail size is best practice and unless you have a high resolution image it s not going to be practical.
The common denominator with all these link thumbnail image sizes is an aspect ratio of 1 91 wide to 1 tall. Why is the mobile image bigger than the desktop news feed. Images can be up to 8mb in size.
Facebook recommends 1200 x 628 pixel size for link share images.
The correct facebook event cover photo size is 1920 x 1080 pixels with a 16 9 ratio. The second reason would be due to no mobile sidebar. 1200 x 628 pixels is ideal. My assumption is that this is first because of tablets.