All the Google account users will now receive a combined storage of 15 GB for its free Gmail, Google+ Photos and Google Drive services. Previously, Google offered 10 GB for Gmail and 5 GB for Google+ Photos and Drive combined. The new limit combines the storage across the three services. So if you use only 1 GB of your Gmail account then you can use the remaining 14 GB as a cloud storage on Google Drive or Google+ Photos.
This offering somewhat exceeds the 7 GB of free storage that Microsoft provides to SkyDrive users. But Microsoft doesn't have any storage limit for its email service Outlook.com
Google is also making updates to the Google Drive storage page, so you can better understand how you’re using storage space.
Source: Google blog