If you have the .torrent file or the magnet link loaded in a client, you can find the exact value here:
: You can use tools like the Torrent File Editor to view the raw metadata, including the piece length (in bytes).
Torrent files are split into small, equal-sized chunks called "pieces" to allow for efficient verification and sharing among peers.
Unable to load "*": Invalid torrent file! <--> Torrent Piece Size - Forums