How to Add File Size Column to SharePoint Online Document Library?

Requirement: Add file size column to SharePoint Online

How to Show File Size in SharePoint Online?
You can add "File Size" column to any list view of SharePoint Online document library to get size of the each file. Just follow these steps to add file size column to SharePoint Online:

• Navigate to the SharePoint Online Document Library
  
• Click on Views drop down in top-right corner area >> Click on "Edit Current View" 
• Search for "File Size" field under "Columns" and include it to the view and set the order in which you want it to appear in your view
• Click on "OK" to save the changes to your view.
  

This adds "File Size" column to the view and shows size of the each document in the view:

Please note, this is size of the file without version history!

You can also get size of the each file from the properties of the file in Explorer view or from SharePoint Designer!