A product key is a 25-character code used to activate Windows. It looks like this:
PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
The location of your product key depends on how you got your copy of Windows:
From an authorized retailer. The product key should be on a label or card inside the box that Windows came in.
A new PC running Windows. The product key will be pre–installed on your PC, included with the packaging the PC came in, or included on the Certificate of Authenticity (COA) attached to the PC.
A digital copy from a Microsoft website. The product key will be in the confirmation email you received after buying it. Or it may be distributed as a digital license if you bought Windows 10, in which case you won't receive a product key.
Free upgrade to Windows 10. If you upgraded to Windows 10 for free from Windows 7 or Windows 8.1, you'll have a digital license instead of a product key. For more info about digital licenses in Windows 10, see Activation in Windows 10.
Article ID: 10749 - Last Review: 31 Aug 2016 - Revision: 46