That is extremely difficult to accurately assess for the period when the Nazis were in power, as Nazi Germany was a totalitarian state without freedom of expression, political freedom, freedom of the press, and other civil liberties that would allow us to gauge public opinion.
Perhaps one way to come at the question is to examine what the average German thought about certain aspects of Nazi ideology after the war, when there was no pressure to adhere to Nazis ideas, when it was in fact rather the opposite, and Nazi ideology was not something one would care to openly espouse. It might be safe to assume that the number of those still adhering to the old ideas was at least equal to (and probably smaller than) the number who had been truly invested in them during the Nazi reign.
From an earlier answer of mine on antisemitism in the immediate post-war years:
Of particular interest are the little known OMGUS (Office of Military Government, US) surveys carried out in the American occupation zone of Germany between 1945 and 1949. These were a whopping 191 public opinion polls (or reports on other expressions of public opinion such as letters to the media) that ranged very widely, gauging Germans' opinion on such diverse topics as "German Attitudes toward the Nuremberg Trials" and "The Problem of Cleanliness in Present-Day Germany".
Particulary grim reading are the responses to the 19 August 1946 "German attitude scale" survey: 37 % agreed that "the extermination of the Jews and Poles and other non-Aryan races was necessary for the security of Germany", 33% that "Jews should not have the same rights as those belonging to the Aryan race". A poll on 3 March 1947 classified the respondents according to their responses on questions gauging attitudes towards the Jews into five categories: those with little bias (20%), nationalists (19%), racists (22%), anti-Semites (21%), and intense anti-Semites (18%). A repeat of this survey in April 1948 showed a slight decrease in the number of anti-Semites and an increase in the number of racists: racists 26%, anti-Semites 19% and intense anti-Semites 14%.
A summary and analysis of the surveys by researchers from the University of Illinois can be downloaded for free from archive.org.