How do I track my data usage?

I believe that rvgrammady is trying to figure how much data she is using with her current household internet so she can figure out how much she can expect to use while on the road. The only faulty part of that scenerio is that she thinks that the current AT&T device is portable and would be used with a campground wifi connection. It would only be usable if she parked somewhere for a long period of time and was able to have a hardwired AT&T line available at her RV.