1. why hard disk is showing less than the actual hard disk capacity.

Ans- https://www.seagate.com/in/en/support/kb/why-does-my-hard-drive-report-less-capacity-than-indicated-on-the-drives-label-172191en/

you can read the above link to understand why hard disk capacity in use is always less than actual hard disk capacity.

To know the actual, hard disk capacity , please perform below steps ->

For Windows 10:

  1. Open any folder -> right click on ‘THIS PC’ -> click on manage
  2.  there you can see the actual hard disk capacity .