Zenity Progress Bar

I made a shell script which uses this command to calculate a sha256 checksum recursive for a directory for example /run/media/$USER/directory:

find . -type f -exec sha256sum {} \; | sort -k 2 | sha256sum

This process takes some time. Meanwhile I want to display a progress bar via **zenity** that shows the current progress according to the command. I tried it with:

find . -type f -exec sha256sum {} \; | sort -k 2 | sha256sum | zenity --progress --title="Checksum"

but it doesn't show any percentages: Thanks for your time! :)