As in how many bytes would be sent?  Games tend to use bandwidth on the order of kilobytes per minute.  I've heard numbers ranging from 1 MB per hour to 20 MB per hour depending on the game.  The bottom line is that an hour of online gaming is comparable to updating your anti-virus daily, and doesn't even register on the same charts as streaming a video on youtube.

The reputation online games have as bandwidth hogs comes from the dial-up era, and even then it was really only the FPS games with large numbers of players.  Games don't even begin to measure up to some of the modern bandwidth hogs, like torrents or video streaming. 

Adsl 1gb cap and its not mine so can't use very much of it in a month.