Now that Google offers unified storage that's shared between Gmail, Google Drive and Google+ Photos, it's more difficult to tell how much storage is used by each service. You can always click "Manage" next to "X GB (Y%) of Z GB used" at the bottom of the page in Gmail and Google Drive, then mouse over the chart.Google Drive has a new feature that shows more details about your storage without having to open a new page: just mouse over "X GB (Y%) of Z GB used" and you'll see something like above.
Courtesy : Google Blog
