Step 1: Login to the cPanel.
Step 2: Click on Disk Usage option under File section.
Step 3: Now you can see a Bar Graph which displays the disk usage information.
Step 4: Scroll Down, you can see the disk usage of each directory.
Step 5: Sort it by clicking on either Name or Disk Usage.
Step 6: It shows the exact size of the each and every file/folder size which is under the file manager.