For any Facebook Page it must have a cover Photo as well as Profile Photo. Most of the users dont know the correct dimensions of the image that they are uploading and end up getting wrong results.
Face Cover Photo Image size:-
Dimesions:- 851*315 Pixels
Users must Upload an image with 851 * 315 Pixels.
i.e. 851 width & 315 height
If you upload the image with less dimesions image will be strecthed.The Cover Photo will be displayed with 640*360 pixels on smartphones.
Facebook Profile Photo Image Size:-
Dimesions:- 180*180 Pixels
Users must Upload an profile photo with 180 * 180 Pixels.
i.e. 180 width & 180 height
Size of the Profile photo must be atleast 180 * 180 pixels.But the photo will appear on facebook page with dimensions 160*160 pixels.Where the profile photo will be displayed as 140*140 pixels on smartphones .