Every HubSpot customer has a Hub ID, which is a unique number assigned to every portal/account in HubSpot. It is also used when connecting certain outside integrations to your HubSpot account.
All users of the HubSpot software can find their HubSpot ID (Hub ID) in the upper-right corner of the screen while logged in. While logged into your marketing or sales account, your Hub ID will appear in the top right corner.
From the HubSpot Sales extension in Chrome, you can click the extension in your browser, then click the gear icon to access your HubSpot account. Your Hub ID will appear in the top right corner (as shown above.)
From HubSpot Sales in Outlook, click Notifications in the HubSpot Sales section of the ribbon to access your HubSpot account. Your Hub ID will appear in the top right corner (as shown above.)