The new Google Plus improvements are still rolling out to users, so you may not see the profile updates just yet. But until then, you can look at Google+'s new large and in charge cover photo, plus the redesigned About page and Reviews tab, right here.
Dimensions/Size of Google Plus Single TimeLine (UpDated):-
You can add a single cover photo of dimensions mentioned below. If you have HD Graphics then you can increase the image size but within the ratio of 480px*270px. The 480px*270px is the minimum required pixel of GooglePlus Profile/Page.
Google Plus Single TimeLine Width: 480 pixels
Google Plus Single TimeLine Height: 270 pixels
Dimensions of Google Plus Profile Pic:-
Profile pictures are larger than before. The dimensions for Google Plus Profile Picture are mentioned below but they will be crop to a circle.(UpDated). Download the below PNG Transparent pic and put ot on your desired profile pic in Adobe Photoshop to confirm the appearence of your pic on GooglePlus.
Google Plus Profile Pic Width: 250 pixels
Google Plus Profile Pic Height: 250 pixels
These all changes are encountred recently so we tried to share it with you as urgen as we can. If you have some more information regarding this topic, you are allowed to share with us. Happy to see you in the comments.