At least 60 GB for a basic install; 100+ GB on an SSD is recommended for full product installations.
Below is a complete guide to downloading and setting up both platforms on a Windows 10 machine. download xilinx for windows 10
To download and install Xilinx software on Windows 10, you must first determine whether your hardware requires the modern or the legacy ISE Design Suite . Vivado supports newer device families like the Artix-7, Kintex-7, and Virtex-7, while ISE is required for older chips like the Spartan-6. At least 60 GB for a basic install;
Windows 10 Pro or Enterprise (64-bit) is officially recommended. download xilinx for windows 10