To be exact: Out of 25,758 km Autobahn in Germany 18,115 km have no speed limit (70.4%) and another 1,608 km (6.2 %) have gantries without speed limit under favourable conditions (construction sites not taken into account).[1]
There are also some other roads that are not included in these figures because they are not classified as Autobahn, but Autobahn-like carriageways. Germany has around 3,350 km of them, a few without speed limit.[2]
That's actually a much higher percentage without speed limit than I expected. I wonder if the stretches without speed limit are usually order traveled and thus less experienced. Anecdotally I used to drive between Bonn and Paderborn a lot and the speed limit would only go away once out of the densely-populated Ruhr area.
