Microsoft revealed Windows 10 now has over 270 million users. The software giant claims Windows 10 is the firm's fastest growing version of Windows for both consumers and enterprises. According to Microsoft's own calculations, the adoption outpaces Windows 7 adoption by 145 percent.
Windows 10's adoption rate has been brisk since it was released thanks to positive buzz and the return of the Start menu: there were 14 million upgrades in the first day, 75 million in the first month, 110 million installs by early October, and 200 million by early January. Developers looking to build Universal Windows Platform (UWP) apps for the Windows Store should be heartened by these numbers—the install base is already quite large, and it's continuing to grow.
Part of the reason why Windows 10 is seeing such a fast adoption is of course because it's a free update and because Microsoft is pushing users of older versions of Windows to upgrade asap.