How big a file is that video you just recorded? How large are the files of those photos you just exported? There are any number of reasons to check the size of a file on your Mac -- the most obvious being so you can free up space by rounding up the largest files and deleting or moving them.
Here are three ways you can check the size of files on your Mac. Folders, too!
Add Size column to List view in Finder
List view is my favorite view in Finder because it offers the most information, including file size. If you don't see a Size column in your Finder window, you can add it by control-clicking on the headers that are visible -- Kind, Date Last Opened and the like -- and clicking Size. You can then click on the Size header to order the list by size. You can also drag the headers to rearrange them.
Bonus tip: You might notice that the Size column is blank for any folders in the List view. You can make the size of folders appear by opening a Finder window with folders in it, clicking View in the menu bar and then choosing Show View Options. At the bottom of the panel that pops up, check the box or Calculate all sizes.
Get Info panel
For any file or folder, you can quickly view its size by control-clicking it and selecting Get Info. In the top right of the Get Info panel, you'll see its size. You can also highlight a file in Finder and use the keyboard shortcut Command-I to open the Get Info panel.
Arrange by Size
If you are looking to free up some space on your Mac, you can easily sort files of any Finder window by size. I have found this is particularly useful for the Recents folder. When I click the Size header to sort by size, it doesn't show me all of my files, but if I click the gear icon at the top of the window and select Arrange By... Size, then I see all of my files sorted into different tiers by file size, starting with 1GB to 10GB files at the top.