It's a rather hard question to answer. Soviet regime have not bothered with supplying Leningrad inhabitants with food, even less they bothered with counting the loses.

However I can tell rough estimations given by Solonin in How Soviet Union won the war (in Russian. The tablets are terrible as multilingual writting goes) . At the beginning of the war city had 3,19 million inhabitants. Before August 27, 1941 about half a million people were a evacuated (in that number 220 000 kids and 164 000 military industry workers) and about 148 000 of refugees came in from the western provinces. However that is official numbers. The most reliable source about the number of people stuck in Leningrad comes from the food cards data and that would put the number of people in the blockade around 2,54 million.

Outside this number are active military personnel who were supplied not via food cards but by military provisions. This is harder to put down, as the number of servicemen in Leningrad Front and Baltic Sea Navy was constantly changing, but orientational number (Solonin extrapolated it from the amount off food rations assigned to army) is about 350 000, leading to a total of 2.9 millions trapped in the blockade.

The number of whose who were able to flee on they own accord and initiative during the blockade (mostly via frozen Ladoga) cannot by established more precisely than "many tried".