Connecting Gmail calendar to Outlook is a popular request and unfortunately, it's not possible unless you use an add-in. However, if you only need a read-only calendar, you can add a Gmail calendar as an Internet Calendar and view your appointments (but not edit or add new appointments).
You need to use the Private ics link in Gmail and add it as an Internet Calendar in File, Account Settings, Internet Calendar.
Another option, if you use Outlook.com, is to subscribe the calendar in Outlook.com. The shared calendar syncs with the Outlook.com account. It's still going to be read-only, but avoids the occasional send and receive errors a subscribed calendar generates.
The Google Calendar Sync Utility utility will work with Outlook (all versions).
- Go to your Gmail calendar
- Right click on the calendar name in the left column and choose Share this calendar
- Click the Calendar Details tab.
- Click the ICAL icon for the Private Address.
- Right click on the URL and choose Copy. Note the HTTPS in the URL. You'll need to remove the S to use the URL in Outlook.
- In Outlook, go to File, Account Settings, Internet Calendar tab.
- Click New.
- Paste the URL in the address field and remove the S from https.
- Click Add. Enter a friend name for the calendar and return to Outlook.
The calendar will sync to Outlook but it is read-only. You can't add appointments in Outlook and have them sync up to the server. Updates made to the calendar online should sync down to Outlook hourly.
Additional articles on using Gmail with Outlook