Normally if you look at your Finder, the column ‘size’ for folders will show ‘-‘. Occasionally, for example when you want to see which folders take up the most space so you can free them up, you would want to see the size of those folders.
So, here is how to do that:
1. On the Finder menu, click on View -> Show View Options (or Command-J).
2. The ‘View Options‘ will be shown as below.
3. Now the only thing you need to do is tick the checkbox next to ‘Calculate all sizes’, and your Mac will start calculating and showing folders sizes.