Refer to our Free Tutorial that will guide through the process of obtaining your google calendar ID:
Step 1: Login into https://www.gmail.com/
Step 2: In your gmail account, click on App link and Select Calendar
Step 3: On the left hand side, you will see My Calendars option, click on it
Step 4: Click on the arrow button to open the drop-down window of the specific calendar
Step 5: Select Calendar settings
Step 6: Under Calendar Details section, you will see your Google Calendar ID
Step 7: Click on Share this Calendar link, then tick mark the checkbox Make this calendar public, and click on Save button