Example

folder 1 100GB
folder 2 120GB
folder 3 10GB > subfolder 1 4GB

If I select folder 2, and folder 3's subfolder, i would like to see that it equals 124GB when I click details

I seen votes for folder size, but this one is specifically for viewing details of multiple selected folders

using ubuntu the chrome extension will not handle a ton of traffic, it'll crash without any error, or prompt to send a crash report. I'd love to know how much of my data was backed up at a glance, otherwise I have to go into each sub-folder>select all>right click>information and basically add up all the sizes and files then compare them to the master folder from which I was trying to upload. Or start a complete re-upload of a particular folder and have to go through the process of replacing folders and skipping files. It doesn't take forever, but as I'm not sure exactly how much of the master folder was successfully uploaded, It can be a gamble for me at times to start another upload and go through the "replace folders-"skip all duplicate files" prompts.
I, myself; and I'm sure so many others are just ridiculously busy all of the time...I'd like to go in even from another device (e.g. Android) and check the total size of the folder I've uploaded. At least if I share it, or plan to re download the data to another device, Ill have some idea of what kind of storage it'll occupy. idk..it just seems kinda obvious and/or necessary.

Thanks OP-This is a much needed...Most needed feature!! imo.

The Windows app is a mystery wondering which folders are being worked on (being uploaded) and how much data in each has been sent / left to go.