Google ,Facebook and twitter profile picture and backcover of size

Google

Google+ Cover Photo  === 1080 x 608.
Google+ Profile Picture  ==1250x250 pixels


Facebook   === profile picture  160x160px  and   180x180px

Page's cover photo == 851*315 pixels  and 640 *360 pixels  on smartphones

Twitter

    Header photo( 1500x500 pixels)
    Profile photo ( 400x400 pixels)