Experience shows that a volume of approximately 2 gigabytes per month is required for daily use.
Of course, this depends on how you use NUNAV.
Currently, NUNAV uses a so-called "environment caching". This means that only the environment data of your last destinations are stored. After the maximum capacity of 200 MB is exceeded, the environment data of the "least visited destinations" are released for the environment data of new destinations.
This way you only load the map material you really need and at the same time you can always navigate with the most current map.
Due to this "environment caching", the data consumption for shorter or recurring routes (for example your way to work) is of course significantly lower than if you drive from Hamburg to Munich today and from Munich to Berlin tomorrow. On these routes NUNAV then loads more data, because more map material is needed.