Storage is calculated as the total size of all mail on the Home page plus all files on the Files page
User storage consists of the storage used by a user plus all of the user’s contacts. Contacts use storage when a user receives files from them and when they upload files to shared folders. The user storage is displayed at the top right of the page.
Account storage is calculated as the total storage of all users in the account. The account administrator can view the account storage on the Account page.
You can expand your account storage limits by upgrading your account type. Click Here for Account Limits