Dropbox is a powerful cloud storage site. A free account gives you 2GB of space to store anything. For many this is enough to store typical Document folder contents. I do not recommend saving pictures and videos as they take up a large amount of space. There are other cloud storage sites to use for them such as the free Google Photos or Amazon Prime.
I upgraded my Dropbox account to 2TB a while ago and have been uploading many files to my Dropbox account over the last couple of years. I wondered how full my cloud storage was and found it difficult to locate the answer as I looked at my account. I could find folders and files and search for anything easily but I did not see how much space was being used. This is the result of my quest.
Open Dropbox and locate your avatar/icon in the upper right corner:
Click the avatar
Now you can see exactly how much space you have used and how much is left. I hope this was helpful for you as well.