Exporting a calendar as ICS: provider by provider
To convert, you first need an .ics file. Here's how to get one out of the common calendars:
Google Calendar
calendar.google.com → gear → Settings → Import & export → Export. You get a ZIP with one .ics per calendar. For a single calendar: pick it on the left in Settings → "Export calendar".
Outlook
Classic Outlook (Windows): open the calendar → File → Save Calendar → choose range and detail → save.
New Outlook and Outlook on the web have no file export. Workaround: Settings → Calendar → Shared calendars → Publish a calendar, copy the ICS link and open it in your browser to download the file.
Apple Calendar and iCloud
Mac: select the calendar in the sidebar → File → Export → Export. iCloud on the web can't export; share the calendar publicly there and open the webcal:// link in your browser with https:// instead of webcal://.
Opening the CSV in Excel
- A double-click usually does it; the file is UTF-8 so accents survive.
- Everything in column A? Your Excel expects a different separator: switch it above and download again, or use Data → From Text/CSV in Excel.
- Google Sheets: File → Import → Upload, let it detect the separator.