How to check what applications are using the most disk space?

Using the Finder, you can sort the Applications folder (or any other folder) by size, and let it calculate the space inside each folder in addition to sizing the flat files.

• The key command Command-Shift-A will open the Applications folder from Finder
• The key command Command-J will Show View Options

Then ensure the checkbox to calculate all sizes is checked. Lastly, click on the size column in the finder window (making sure you are in list view (Command-2) to sort by size. Keep clicking to reverse the sort order if the small applications get sorted to the top.

You will also want to look at your home folder as well as the /Library folder to see if some applications have large media files that you might be able to delete if you don't do movie editing or need all the Garage Band loops for example.

Try About this Mac / More info / Storage and you'll get something like this: