Microsoft Remote Desktop Bandwidth Usage
With the recent advancements to the Task Manager, incorporating Resource Monitor, you can easily see the bandwidth usage from Terminal Services.
In short, it all depends on the settings you have used and what you're doing in the remote session. More actions require more repaints. Below are two shots I've taken while in an RDP session to a Windows 2008 R2 server.
The first screenshot, only Resource Monitor open (~3.6KBps):
The second, a YouTube video streaming (~951KBps):
Hourly bandwidth consumption at rates like these can vary from ~12M to 3.4G+. Unless you are watching video over RDP, the higher end of the ladder is highly unlikely. For normal activity at 1024x768 resolution with standard settings I'd estimate about ~25M per hour.
It depends on which version of RDP you are using and what settings you have. Take a look at this 2008 test report by Microsoft.
Table 11 and Chart 11 show the bandwidth consumption (in KBps) between a Remote Desktop Connection client and different server operating systems. The tests were conducted at 16-bit color depth with themes turned off.
RDP uses around 80kbps (or more if printing or sound is included)