The length of Windows 10 Product key is 25 characters long which you need to insert after installing Windows 10. Moreover, we always recommend to Activate Windows 10 Pro Product Key. When you download the Windows Product from Microsoft or other product, the first thing you need to do is to Windows 10 Upgrade Product Key. Windows 10 Upgrade Product Key – Activation in Windows 10Īn activation key is also known as the product key.