How to Quickly Change File Extensions for Multiple Files on a Mac

Changing a file extension (the three or four letters after the period, such as .jpg or .txt) tells the operating system which application it should use to open the file. Sometimes, you may receive a batch of files with the wrong extension, or you might need to quickly rename hundreds of .jpeg files to .jpg for a strict web server requirement.

Manually clicking on each file, hitting Return, deleting the old text, typing the new text, and confirming the warning prompt is an incredibly tedious process. Fortunately, macOS Finder has a built-in batch renaming tool that makes this process nearly instantaneous.

Understanding the Warning

Before proceeding, it is important to understand that simply changing a file’s name from video.mp4 to video.mp3 does not magically convert the video into an audio file. It simply tricks the Mac into trying to open the video with a music player, which will likely result in an error. You should only use this method when you know the underlying file data is correct, but the text label (the extension) is wrong or needs standardising.

How to Show File Extensions

Before you can change an extension, you must ensure your Mac is actually displaying them. By default, macOS often hides file extensions to make filenames look cleaner.

1. Click on the desktop to ensure the Finder application is active.
2. Click on Finder in the top-left menu bar and select Settings (or Preferences on older versions of macOS).
3. Click on the Advanced tab (the gear icon).
4. Check the box next to Show all filename extensions.
5. Close the Settings window.

How to Batch Rename the Extensions

Now that you can see the extensions, you can use Finder’s powerful rename tool.

1. Open a Finder window and navigate to the folder containing the files you want to change.
2. Select all the files you wish to modify. You can click and drag a box over them, or click the first file, hold the Shift key, and click the last file.
3. Right-click (or Control-click) on any one of the highlighted files.
4. Select Rename… from the context menu.

A new interface will slide down from the top of the Finder window. This is the bulk renaming tool.

1. In the first drop-down box on the left, ensure Replace Text is selected.
2. In the Find: box, type the current extension exactly as it appears, including the period (e.g., .jpeg).
3. In the Replace with: box, type the new extension you want to apply, including the period (e.g., .jpg).
4. Look at the bottom left of the tool; macOS will provide a live preview of what the new filename will look like.
5. If the preview looks correct, click the blue Rename button on the right.

A warning prompt will appear asking if you are sure you want to change the extension, warning you that it may cause the document to open in a different application. Click Use .jpg (or whatever your new extension is) to confirm.

Finder will instantly apply the change to all the selected files simultaneously, saving you significant time and effort.