bandwidth calculator?

Soon I'm going to be limited to 3GB a month, which is nearly nothing in my eyes..

are there any bandwidth calculators that will count everything in a months use?

they have some on websites, but not actually software that will give you genuine results... i need to know quite badly because if i go over it's a lot of money.

That's unfortunate...OS-X Lion download is 4GB in size.
I am looking for something that 'shows' my bandwidth speed...any help out there?

I use the dashboard widget iStat Nano... it works well.

I use Surplus Meter. Going to check that Dashboard Widget. Looks interesting.