If you are using Apple iCloud, the folder sizes are not shown by default when they are not downloaded to your Mac. Doing the following will show all the folder size whether they are downloaded or present only in iCloud.
- Using Finder, Access the iCloud drive.
- Navigate to folder in iCloud drive. As you can see in the below screenshot the folders size are not shown as they available in Cloud.
- Click View menu option and select “Show View Options” from the menu list.
- Tick the checbox with the label “Calculate all sizes”
Now the Finder should show all the folder size even if they are present in Cloud only.