The size of a Windows 10 ISO file has been much in discussion since users need to determine the space needed to store the ISO file, be it on a disc or s system. The reason is that the size of the ISO differs across versions of Windows 10 and also the build you intend to download.

Usually, the size of an ISO file increases with every feature update launched by Microsoft. For an estimate, an ISO file I downloaded for Windows 10 had a size of 4.07 GB. Other users have placed the figure anywhere between 3GB to 5GB.

Thus, it is advised to reserve a space of 5GB if you are planning to download the latest ISO file for Windows 10.