[tor-relays] Relay bandwidth accounting

I just set up a new non-exit relay and in going through information to set up, I came across the T-shirt for contributing and in addition to running for 2 months it says "if you're not an exit but you average 500 KBytes/s traffic." What would be the best way to keep accounting of the traffic my relay is passing? I know of the metrics.torproject.org, is that all the project would need?