Exactly what size does my Google+ cover picture have to be when I upload my photo from my PC?.
Your looking at a standard size of 480 x 270 when uploading the picture to Google Plus. That’s the smallest size at least. It’s recommended to upload at least 1080 x 608, or even up to 2120 x 1192. Of course it might take a bit to upload depending on the file size, those picture sizes tend to be bigger than normal. At the top of the screen, view your cover photo and click on “Change Cover”.
It sucks trying to upload a photo after looking for one on Google Images that you want to use. Then after failing to upload the image you want, having to go back and find another image that is the right size. I find myself using Paint.net to resize most images, or crop them to my liking and making my preferred images the right size.