@saibot: See https://winscp.net/eng/docs/ui_transfer_custom#calculate:

Note that when using multiple connections, the calculation does not add time to a transfer, as directories are not listed again for the transfer itself.

Please understand that it's not something that can be skipped. WinSCP needs to list the files to download, no matter what. Any client needs to do that. The only difference here is that for background transfers, it lists all folders in advance, while for foreground transfer, it lists one folder, downloads its files, lists another one folder, downloads its files, etc. In the end, it does not matter. The overall operation takes the same time. With background transfers just takes longer before the first transfer happens.
I might change the label to "Listing" instead of "Calculating" to make this more clear:
https://winscp.net/tracker/2026

I don't get this (cancelling the calculation)...would be great.
I am looking for the option to use background transfers but at the same time avoid the size calculation.

Currently, even if you disable multiple connections and set parallel connection only to 1, and you have only one background transfer, AND you have disabled the "Calculate total size checkbox" in transfer settings: still the "size calculation" takes place and takes ages.

This is so frustrating.

Even if there is the option to not use the background transfer at all (only then, size calculation does not happen - but you cannot handle multiple projects then at the same time and you don't "see" the current transferred files (like on background connection dialogue or like FileZilla for example handles it)....):

So, Please:
Can you add this as a feature request or provide an option to abort the size calculation - while at the same time using background transfers?

There's no "size check". WinSCP just retrieves the list of files to download. As documented here, it does not add any time to the overall transfer duration:
https://winscp.net/eng/docs/ui_transfer_custom#calculate
The only difference is that the order of operations is different. So it takes longer before the first transfer actually starts. But in the end it does not matter.

Hello.
I have folders on server around 1Tb with about a million small files. I'm trying to download it, but size check takes a lot of time (tens of minutes). I can download it in foreground mode without size check, but in foreground mode it's going with only one connection (~2-3Mb/s). To use few connections (four for 8-10Mb/s) I need to put transfer in background mode, but in the background mode is not possible to disable size check.
Is it possible to add option to disable size check in background mode or option to use >1 connection in the foreground mode?