Google, with zero warning as usual, has changed the dimensions and style of the Google Plus cover pages.
Frankly, I think they are way to big and turn previously nice looking covers into garbage. They take up nearly the whole page and force the content below the fold. A violation of their "quality" guidelines?
Gripes aside, the new image size can be as large as 2120px by 1192px according to Tech Crunch.
However, the minimum size has to be 480px x 270px. In typical Google fashion there is no documentation and their cropping tool is an oddity only Google could make.
After an hour or so of trial and error, I have come up with the following template that seems to work and compensate for the auto-compression pixelation in the final presentation. It also takes into consideration the "gutters" and the new default gradient fade applied to the lower horizontal edge of the image. (Can you say ugly? Hope you like grey gradient fades because you forced to have one now.)
Ready? Here we go.
1) In your favorite image editor, create a canvas that is 1333 px by 750 px. Set the DPI to 200.
2) Set a "guide" for the left gutter to be 10px wide and the right gutter to be 23 px wide.
3) There does not seem to be a top gutter/margin, but the footer gutter/margin should be set 160 px height to accommodate for the default gradient fade that Google adds to all covers.
4) These gutters/margins now reduce your work space to 1305 by 590 pixels.
5) As for the profile picture, the minimum upload size is 250px by 250px, but will have a circle mask auto-applied to it. When it's loaded into the cover, it will re-sized down to 120x120. To simulate the position of the 120x120 profile image, position a 120x120 circles left edge 239 pixels from the bottom left edge of the canvas. Set the top edge of the circle 145 pixels from the bottom edge of the canvas.
6) When your images are ready save a jpg with NO COMPRESSION. When you upload to Google, Google will compress the image.
Hope that helps. If you use this tutorial, please do share a link to final work on a live Google Plus page. Also, if you have additional tips or template dimensions that work for you, please do share.
Seems I forgot to consider responsive design. Here's another tutorial you should check out as well if you have mobile users to your Google Plus page: Google Plus New Cover Responsive Guide
Author: Michael Zittel