If you recall, the current (old) Twitter design looked something like this.
Essentially, the main difference between the new and old designs are the new design highlights the cover photo more heavily and basically gets rid of the background image.
In the new design, the cover photo changes dynamically depending on your screen resolution. It's always anchored to the left, but the top and bottom of the image are not fixed. There seems to be some odd padding in effect.
After playing around with ti for some time, though, I have found out its secrets.
I've found that the perfect dimensions to use are a 2450 x 814 image and concentrate the most important elements within 2450 x 562 range from the center (see the guide below).
Bellow are some templates you can download from what I have above. It includes a black PNG image with the correct dimensions for the new Cover Photos (2450 x 814 pixels) as well as a .psd with general guidelines of where you should center the content of your image.
Thank you! like lots!, been looking for the right size of the new header everywhere and all other blogs are wrong as hell. Great job!
Thanks, Laiden! Glad this post was helpful for you.