In Numbers 1:19 through verse 46 it tells of the census Moses took.
Num 1:19 as the LORD commanded Moses. So he listed them in the wilderness of Sinai.
At the end it says this:
Num 1:45 So all those listed of the people of Israel, by their fathers' houses, from twenty years old and upward, every man able to go to war in Israel—
Num 1:46 all those listed were 603,550.
So, this was only men 20 years and older and able to go to war. It would be common sense to figure there is at least one female for every man. Let's just average it out to 1 million two hundred thousand. 1,200,00. Do you suppose they had no children under 19? That could easily be another million or so. But it also says:
Exo 12:38 A mixed multitude also went up with them, and very much livestock, both flocks and herds.
This mixed multitude would have been Egyptians and other non-Jews who were slaves along with the Jews. I can easily see 3 million people.
It seems incomprehensible for that many people trudging through the wilderness. I just looked it up and the population of Denver, Colorado was 715,522 at the 2020 United States census. So these guys would have been double or even triple that number.
Imagine how many tons of Manna God would have had to provide everyday to feed them!