Getting your social media profiles presentation right can sometimes be hard, here are recommendations to the right dimensions for high quality images popular sites.
Youtube
Banner: 2560 x 1440
Avatar or profile picture: 800 x 800
Thumbnail: 1280 x 720
Header/banner: 1500 x 500
Avatar or profile picture: 400 x 400
Profile picture: 340 x 340
Profile banner: 1640 x 624
Profile picture: 110 x 110
Google +
Profile picture: 800 x 800
Banner or header: 2560 x 1440
All sizes are in pixels (px)