Facebook quietly crops and re-compresses any image that isn't the right size, which is why cover photos turn out blurry and post images get cut off. The fix is to resize each picture to Facebook's exact pixel dimensions before you upload it. You can do it in a few seconds with Pikdee's free Resize Image tool — everything runs in your browser, so your photos are never uploaded to a server.
Use 1200×630 pixels (a 1.91:1 ratio) for a shared or feed post. That is the size Facebook displays at full width on both desktop and mobile, so your image stays sharp and isn't cropped or letterboxed.
A Facebook cover photo displays at 820×312 pixels on desktop and 640×360 pixels on mobile. Upload at 820×312, or a larger image with the same 205:78 ratio (for example 1640×624), and keep key details centered so nothing important is cut off on either device.
No. Resizing only changes the pixel dimensions. As long as you resize to Facebook's recommended size instead of uploading a huge file for Facebook to shrink, the image stays crisp — and often looks better, because Facebook then applies less of its own compression.