Used to activate new installations of Microsoft's OS, the Windows product key is something you probably don't think about . . . until you really need it. Whether you're about to do a clean install of Windows 11 or 10 on your existing PC or you need to move the license to a new computer, you'll probably need this 25-character, alphanumeric code.
As we've noted elsewhere, the best way to get Windows 11 for free is to reuse a Windows product key you have either on the current computer or another you own and aren't using anymore (note that "OEM" keys may not let you reuse them on different hardware). But unless you bought a copy of the OS at retail and have it written down somewhere handy, you may not know the code. Fortunately, there are several ways to find your Windows 10 or 11 product key and they're all easy. These methods were retested and worked as of March 2025.
