I was present at anti-Pershing II as well as a pro-Pershing II demonstrations in Bonn (former West German capital) in the early 1980s. And I saw the pictures on TV afterwards. These had been the biggest demonstrations in West-Germany at least since WWII. Numbers of participants then were undisputedly both anti as well as pro more than 300,000.
From what I've seen on youtube, if you ask me, there were at least 500,000 in in Berlin. The number of 1,300,000 is said to be a number of the police department.
German speaking alternative media folks are expecting a general Verbot to demonstrate, and are also expecting even larger demonstrations to follow. Demonstrators are said to have not only arrived from all over Germany, but also from various neighbouring countries, and even Spain and Italy.