Try this 1
If that particular folder properties is showing you the correct size then check if
the files are not in hidden mode.
Click on Start --> Run --> Type control folders and press Enter.
[If you are using "Window Vista or 7" then click on
Start --> In search box, type control folders and press Enter]
"Folder Options" will be opened. Click on the "View" tab.
Select the option "Show hidden files and folders" and uncheck the check box
"Hide protected operating system files" --> Click on OK.