How do I measure the amount of network traffic that passed my debian installation?

So my raspberry pi is acting as a Router and Web/Mail/FTP/SQL/Media/Clash of Clans/Home server right now and I'm looking for a way to monitor the consumed bandwidth, much like NetWorx for windows. I found some solutions (webmin's bandwidth monitoring) but it takes up too much space (several GB) and CPU time. Can you recommend me something that only measures the current bandwidth speed and the amount of data that passed through, without using the logs? (Webmin's bandwidth monitoring turns on IPTables' packet logging then later analyzes the logs, which consumes too much disk space and CPU) This is networx bandwidth summary Networx average speed