Hungary - situating in the centre of the continent - is one of the most loaded transit country in Europe. There are many TEN-T corridors crossing the country. The external cost coming from the heavy road transport is very high. On the other hand there are other eco-friendly transport modes available like railway or inland navigation. In the general approach navigation is an untrustworthy technology and has uncertain capacity. The present study tries to change this opinion bringing new turn of mind. There are more way to define the waterway capacity. Because of the dynamic hydrological changes the cross-section has no stability, like road or railway cross-section. The paper shows these differences and deals with ,theoretical and planned capacity ,capacity factors ,flexibility analysis ,question of measure units ,time factor. Copyright © FSB, Zagreb, Croatia, 2014.