Most of us use Facebook to post our photos. However many of us especially photographers are not happy with the output quality given by Facebook after it compressed the photos. I have done a little research and I have found out that there are certain supported sizes by Facebook.
Resize your photo to one of the following supported sizes:
Regular photos: 720px, 960px or 2048px wide
Cover photos: 851px by 315px.
Anything apart from the above image sizes, Facebook will resize them.
To avoid compression when you upload your cover photo, make sure the file size is less than 100KB
Save your image as a JPEG with an sRGB color profile.
Also in the web the highest resolution is 72 pixel/inch. So even if you put a higher resolution than 72, it will not make any difference and will only increase your file size. However to print an image the recommended resolution is 300ppi.
I hope this works for you.