What Is an ICS File?

How to open, edit, & convert ICS & ICAL files

Screenshot of several ICS files that open with Microsoft Outlook in Windows 10
ICS Files.

A file with the ICS file extension is an iCalendar file. These are plain text files that include calendar event details like a description, beginning and ending times, location, etc. The ICS format is typically used for sending people meeting requests but also a popular means for subscribing to holiday or birthday calendars.

Although ICS is much more popular, iCalendar files may instead use the ICAL or ICALENDER file extension. iCalendar files that just contain availability information (free or busy) are saved with the IFB file extension or IFBF on Macs.

ICS files that aren't iCalendar files may be either IronCAD 3D Drawing files or IC Recorder Sound files created by a Sony IC recorder.

ICS is also an acronym for a few technology terms that have nothing to do with calendar files, like Internet Connection Sharing, Image Capture Server, and IEEE Computer Society.

How to Open an ICS File

ICS calendar files can be used in email clients like Microsoft Outlook, Windows Live Mail, and IBM Notes (formerly known as IBM Lotus Notes), as well as most popular calendar programs like Google Calendar for web browsers, Apple Calendar (previously called Apple iCal) for iOS mobile devices and Macs, Yahoo! Calendar, Mozilla Thunderbird's Lightning Calendar, and VueMinder.

As an example, say you want to subscribe to a holiday calendar like those found on Calendar Labs. Opening one of those ICS files in a program like Microsoft Outlook will import all the events as a new calendar that you can then have overlaid with other events from the other calendars you're using.

However, while using a local calendar like that is useful for things like holidays that won't change all year long, you might instead want to share a calendar with someone else so that the changes anyone makes is then reflected in the other people's calendars, like when setting up meetings or inviting people to events.

To do that, you could store your calendar online with something like Google Calendar so it's both easy to share with others and also simple to edit wherever you are. You can import the ICS file into Google Calendar which lets you share your calendar through a unique URL and edit the .ICS file with new events.

A regular text editor like Notepad can open ICS files, too — see others in our list of the Best Free Text Editors. However, while all the information is intact and viewable, what you'll be looking at isn't in a format that's the easiest to read or edit. It's best to use one of the above programs to open and edit ICS files.

ICS files that are IronCAD 3D Drawing files can be opened with IronCAD.

For ICS files that are IC Recorder Sound files, Sony's Digital Voice Player and Digital Voice Editor can open them. Windows Media Player can as well, so long as you install Sony Player Plug-in.

If you find that an application on your PC does try to open the ICS file but it's the wrong application or if you would rather have another installed program open ICS files, see How to Change the Default Program for a Specific File Extension for help making that change in Windows.

How to Convert an ICS File

You can convert an ICS calendar file to CSV for use in a spreadsheet program with the free online converter from Indigoblue.eu. You may also be able to export or save an ICS calendar file to another format by using one of the email clients or calendar programs from above.

You can also convert an ICS file to PDF or XLSX with the online ICS Converter tool. However, the converter is free for only ICS to TXT conversions; all the other supported formats cost a couple dollars.

IronCAD can surely export an ICS file to another CAD format through a File > Save As or Export menu option.

The same is true for IC Recorder Sound files. Since they contain audio data, it wouldn't be surprising if Sony's programs linked above could convert the ICS file to a more common audio format.

Still Can't Open the File?

The most common reason an ICS file can't open even after trying all the suggestions above, is because the file isn't really a calendar file. This can happen if you've misread the file extension.

For example, ISC files could easily be confused for ICS files even though they're actually Xilinx Device Configuration files. ISC files cannot open with a calendar program or online calendar service, but instead are used with Xilinx's ISE Design Suite.

Another suffix that could have you thinking you have an ICS file is LCC, which is for Capture One Lens Cast Correction files. These files open with Capture One from Phase One.