Go to /Applications and, if you are in List View, the size will appear in the Size column. Otherwise, you can always select the application's icon and go to File>Get Info (or press Command-I).

Jon

macOS 11.7.10, iMac Retina 5K 27-inch, late 2014, 3.5 GHz Intel Core i5, 1 TB fusion drive, 16 GB RAM, Epson SureColor P600, Photoshop CC, Lightroom CC, MS Office 365