—  Updated in January 2018— Since April 2014 Twitter has used one profile design, which still prevails to this day, that clearly looks very (VERY) similar to Facebook. The intent of this change, together with that of the homepage, has given a lot more importance to images and buttons in order to give users an experience similar to that which they have on their mobile devices.

And now, Twitter Image Sizes 2018

From Twitter’s Help Center, they suggest the :

– Twitter Profile Picture Size: 400 x 400 px – Twitter Header Size (or cover photo) : 1500 x 500 px

Credit: https://postcron.com/en/blog/social-media-image-dimensions-sizes/