Understanding File Extensions

Your computer has many different types of files on it, and each one has its own file extension. A file extension is a three- or four-letter identifier found at the end of a file name and following a period. These extensions tell you about the characteristics of a file and its use. In this lesson, we'll go over some examples of these extensions, as well as how to determine a particular file's extension.

Watch the video below to learn more about files and extensions.

Examples of file extensions

File extensions allow the computer to know what kind of file it is dealing with. Here are some common ones:

• JPEG (.jpg or .jpeg): Used for images and photographs (e.g., image.jpg).
• Word Document (.docx): Used for Microsoft Word documents. Older versions use .doc (e.g., CoverLetter.docx).
• MP3 Audio (.mp3): Used for music and audio files (e.g., rhyme_rap.mp3).
• Excel Spreadsheet (.xlsx): Used for Microsoft Excel spreadsheets. Older versions use .xls (e.g., budget.xlsx).

Hidden file extensions

Some operating systems hide file extensions by default to reduce clutter. It is possible to show the file extensions if they're hidden.

You can also usually tell what the file type is by looking at the file's icon. For example, the Word document looks like a file with a W in the corner, while an Excel spreadsheet looks like a file with an X in the corner.

File extensions also tell your computer which applications to use when opening that file. Sometimes you may want to use a different application to open that file by right-clicking it and selecting "Open With."

FAQs

Can I rename a file extension to convert the file?

No. Simply renaming a file from "image.jpg" to "image.png" does not convert the file format. It might actually make the file unreadable. You must use file conversion software or "Save As" in an editor to change the format.

What is a .zip file?

A .zip file is a compressed folder that can contain one or more files. It is used to reduce the overall file size for storage or emailing. You usually need to "unzip" or "extract" it to use the files inside.

What opens a PDF file?

A PDF (Portable Document Format) is usually opened by Adobe Acrobat Reader, but most modern web browsers like Chrome and Edge can also open them.

Why can't I see the file extension on my computer?

Windows and macOS often hide common file extensions by default to keep the interface clean. You can enable them in the "View" tab of File Explorer (Windows) or Finder Preferences (Mac).

What is an .exe file?

An .exe file stands for "executable." It is a program file used to install or run software on Windows computers. Be careful opening .exe files from unknown sources, as they can contain viruses.