I tried googling “How big is my OneDrive folder” and couldn’t find a quick and easy answer, so I’m writing my own! I hope it helps you.
First, locate the blue cloud icon [1] in the lower right corner of your screen and click on it.
Next, click on the Gear icon [2] in the upper right corner of the menu that appeared.
Third, click on Settings [3] from the Gear icon menu that appeared.
The next screen that pops up will show you the storage amount and the total you have available.
