You can use Outlook on the Web to determine how much storage space you have in your Microsoft Outlook account by following these instructions:

1. Log in to your Outlook on the Web account at portal.office.com.
2. Select the gear icon at the top-right corner of the Outlook window to open the Settings menu.
3. Select View All Outlook Settings.
4. Select the General tab on the left.
5. Select Storage. Your mailbox usage will appear on the right.