How to tell how big one time machine backup is from another?

Inside each snapshot, there is a file named .Backup.log ... inside there, you will see the size of each snapshot.

Look for something that says:
Space needed for this backup: 676.1 MB (173088 blocks of size 4096)

Looking on the filesystem level is only possible with some scripting, since it makes very heavy use of hard links.

 

go to time machine preferences when it's doing a backup...it'll show you a progress bar and how big the backup is.

 

Not to my knowledge

 

Time machine backup log

You can view the log in Time Machine itself, just open Time Machine, locate any backup finder you like, and select your machine in the browser. You should see a short list of entries, the first of which is likely Backup.log. Double click to read the log for that backup.