This article explains how to back up all of your Google Calendar calendars to ICS files, plus how to export events from a single calendar. Instructions apply to Google Calendar on the web.
How to Import Ics into Google Calendar – Open your Ical file
Google Calendar is an excellent time management and scheduling calendar service that lets you plan and share events across the web, mobile devices, and desktop applications. While Google Calendar has a rich feature set, there may be times when you want to reuse a Google Calendar event elsewhere or share it with others. In that case, export your Google Calendar data to an ICS file, a format supported by most scheduling and calendar applications.
After you have backed up your calendar data to an ICS file, you can import the calendar events directly into another program, such as Microsoft Outlook, or save the file for backup purposes.
Open Google Calendar on your computer.
