How do I find out which product key was used to activate Windows?

I have several retail copies of Windows 7. Normally I make a note of which product key was used to activate which PC. Unfortunately, I slipped up.

I've just reinstalled Windows 7 on a PC, and I'd like to activate it. How do I audit my other PCs to find out which product key I used, so that I know which key to use for the reinstall?

The value in Computer Properties (that looks like 00123-012-1234567-12345) is not the one I'm referring to. This is the "Product ID".

I'm referring to the key that would normally be on the DVD case; the one that looks like AAAA1-B2222B-C3CCC-4DDDD-EEEE5. This, confusingly, is sometimes referred to as the "Product Key".

Answer

For Windows 7, 8, 10 you can use the slmgr command line program to reveal a portion of the key to help narrow it down.

1. 
   

   Open Start Menu, then type:

   
   

   cmd

   
   


2. 
   

   Right click CMD application in the search listing

   
   


3. 
   

   Then click "Run as administrator"

   
   


4. 
   

   At the command prompt, type the following and press enter:

   
   

   slmgr -dli

   
   


5. 
   

   Wait for a little window to appear and then look at the value to the right of "Partial Product Key:"

   
   

   

   
   


6. 
   

   Compare with and match to your windows product keys at hand. Note that this reveals the right most part of the ................-3V66T