OS X: Show exact file size in Finder
Solution 1:
Whenever you have a file selected, you can press ⌘I to bring up "Show info", that will tell you, among other things, the exact filesize in bytes. I do not know a way to get that information in the column view, though – sorry.
Solution 2:
I don't think there is a way to do this. Why do you need the exact size? What problem are you trying to solve?