Why did my download claim to only take 4.6 GB, and the file itself takes up 4.9 GB?

I am selling my old laptop and I want to put Windows 10 on it since it should sell better that way.

I downloaded Windows 10 using the chromium web-browser and it said the file was only 4.6 GB. I have a DVD-RW that has 4.7 GB of space, but when I check the properties tab of the file, it says the file takes up 4.9 GB. My disk-writing software, brasero, refuses to burn the file to the disk because the file is too large.

Why did the file say it was only 4.6 GB when I downloaded it? Is there something I can do to install Windows 10 on my Ubuntu 18.04 laptop?

I cannot use a flash drive because the USB ports on the laptop are bent.