How to Change a File Extension in Windows

This page shows you how to change the name of a file extension in Windows XP and Windows 7. For example, you might want to change a file called mypage.php to mypage.html, or myvideo.vob to myvideo.mpg. We use Windows 7 for this example but the same process applies to most versions of Windows.

Changing a file extension should only be done if you are confident it's the right thing to do. There are many reasons for changing an extension — sometimes it's fairly straightforward, sometimes it's a bit of a gamble. When you change an extension, one of three things is likely to happen:
 

•  It won't make any difference to how the computer deals with the file.
•  It will enable some programs to recognize and work with a file, while other programs may no longer recognize it.
•  It will not have any useful effect and the file will no longer open properly.

Step By Step Process:


The first thing to do is open Windows Explorer (or My Computer) and view the file you wish to change. We will use the example of a file called "a_mercedes_emerging.php" which we want to change to "a_mercedes_emerging.html". It looks like this in Windows Explorer:

 
 
At this stage you might notice that your file does not appear to have an extension (in the above example it would simply be called a_mercedes_emerging). This is probably because you have Windows set to hide extension names. Go to Tools > Folder Options, then click the View tab. Uncheck the box titled "Hide extensions for known file types" and click on the Apply button like so:
 

Click OK. Now you should be able to see the file extensions for all files. Right-click the file name and select Rename. Enter the new extension like so:

After entering the new extension, hit the Enter (return) key. Windows will give you a warning that if you change a file name extension, the file might become unusable. This is quite safe — if the file does stop working you can always change the extension back (just make sure you remember what it was!).


It's also possible that you might get another message telling you that the file is "read-only". In this case either say yes to turning off read-only, or right-click the file, select Properties and uncheck the Read-only box.

Note: Windows treats file extensions as case-insensitive, i.e. .RTF is the same as .rtf. However other operating systems do not, and will treat myfile.RTF and myfile.rtf as two different files. Therefore it is good practice to always treat your files as case-sensitive for maximum compatibility. This is especially crucial if you are going to use the files on the Internet. We strongly recommend that you get into the habit of using all lower-case letters for all file names and extensions.