How to Change a File Extension, and Why Renaming Doesn't Convert

The job application portal wants a JPG, but your photo is called “IMG_2041.heic”. So you change the extension to .jpg, upload the file and still get “File format not supported”. That’s because renaming only swaps the label, not the content. Here you’ll learn how to change file extensions on Windows, Mac and your phone. And you’ll see when that’s enough and when you need to really convert an image.

Show file extensions

Windows hides known extensions like .jpg or .pdf by default. Before you can change an extension, you need to make it visible.

• Windows 11: Open File Explorer, click View at the top, then Show, and check File name extensions.
• Windows 10: Open File Explorer, click the View tab at the top and check File name extensions.

From now on, your photo is no longer called “Vacation” but “Vacation.jpg”. The setting applies to all folders.

How to change a file extension in Windows

Take the warning seriously. Windows doesn’t know whether the content matches the new extension. If it doesn’t, the file won’t open properly afterwards. You can always undo it, though, by typing the old extension back in.

When is renaming enough?

Only when just the name of the format differs, but the content is the same.

Why JPG and PNG are different formats in the first place, and which one you need when, is explained in the guide JPG vs PNG.

How to really convert images

For a single image, the built-in tools are often enough. On Windows, open the image in Paint, click File, Save as and choose the format. On a Mac, open it in Preview and choose File, Export.

This has three limits:

• One image at a time: Paint and the Photos app only save one image at a time. With twenty photos, that takes a while.
• HEIC on Windows: Paint only opens iPhone photos once you’ve installed extensions from the Microsoft Store.
• Transparent areas: JPG doesn’t support transparency. Many programs turn those areas black, and you can’t pick the color.

It’s faster in your browser. You select all your images at once and download them as a ZIP or one by one. Your images stay on your device the whole time.

• iPhone photos: HEIC to JPG
• Screenshots and graphics that are too large or need to be JPG: PNG to JPG, with a white instead of black background
• A program or form wants PNG: JPG to PNG

Where the HEIC format comes from and why Windows won’t open it is covered in the guide What is a HEIC file.

“File format not supported”: what to do?

You see this message when a program, portal or app can’t handle the content of a file. With images, there’s almost always one of three reasons:

1. The image is HEIC or WebP. Many forms only accept JPG or PNG. Convert the image instead of renaming it.
2. The extension was changed by hand. The portal checks the content and sees that the “JPG” isn’t one. Rename the file back and convert it properly.
3. The file is too large. Some portals wrongly report this as a format error. A PNG photo saved as JPG is often only a fifth of the size.

If you get the message for a video in WhatsApp, it’s usually the video codec. Filemanta doesn’t have a tool for that.

Change multiple file extensions at once

For many files, Windows has Command Prompt.

1. Open the folder with the files in File Explorer.
2. Click into the address bar, type “cmd” and press Enter.
3. Type, for example, ren *.jpeg *.jpg and press Enter.

All files ending in .jpeg now end in .jpg. Same rule here: this only changes the names. ren *.png *.jpg doesn’t turn PNG images into JPGs. For that, you need a converter that handles several images at once.

How to change a file extension on a Mac

1. Open Finder, click Finder in the menu bar at the top, then Settings.
2. Choose Advanced and check Show all filename extensions.
3. Click the file, press Return and change the extension.
4. macOS asks you to confirm. Choose Use .jpg (or whatever the new extension is).

For many files at once, select them, right-click and choose Rename. There you can replace text, for example “.jpeg” with “.jpg”.

How to change a file extension on iPhone and Android

• iPhone: Open the Files app and tap the More button (…) at the top right. In the view options, turn on Show All Extensions. Then touch and hold the file, tap Rename and change the extension.
• Android: Open Files by Google or My Files (Samsung). Touch and hold the file and choose Rename. The extension is usually already visible. Your phone warns that the file might not work afterwards.

The same rule applies on your phone as on your computer. A renamed HEIC photo is still HEIC. To convert it, just open the tool in your phone’s browser.

If something goes wrong

• The file is suddenly called “photo.jpg.txt”: Extensions were hidden, and you only changed the visible name. Show the extensions and delete the extra “.txt”.
• The file won’t open anymore: Rename it back to the old extension. Nothing is lost when you rename a file.
• You just want a different program to open it: Then don’t change the extension, change the default app. Right-click the file, choose Open with and then Choose another app.

• The file extension is just part of the name. It doesn't change what's inside the file.
• In Windows 11, you show extensions under View, Show, File name extensions.
• Renaming only works when the format is the same, like .jpeg to .jpg or .jfif to .jpg.
• Renaming .heic, .png or .webp to .jpg doesn't create a real JPG.
• You truly convert images with Save as or a converter in your browser.
• If a file won't open after renaming, just rename it back.