Microsoft’s official Media Creation Tool and ISO file require at least 8 GB of free space on the USB flash drive. However, a freshly created Windows 11 bootable USB will actually use about 5–7 GB, depending on the edition (Home, Pro, etc.) and included updates.
Because USB drives are measured in binary (where 1GB = 1024MB) and manufacturers often measure in decimal, an "8GB" drive usually only has about of actual usable space. windows 11 usb size