The most recent numbers being quoted by the Canadian government are 1 in 160 have a form of PDD.
Some numbers have it as low as 1 in 10,000.
Really it is widely debated, I think the 1 in 160 is more realistic. I think it might be as high as 1 in 100 have ASD.
The thing to remember though, is that there are other non verbal learning disabilities too, so we are not the only ones that struggle with communication. You don’t have to be autistic to miss out on social clues among other things.
It also is a spectrum, sort of like vision, you can have 20/20 vision, or anything in-between that and being blind. At some point, a line is drawn, and the person is said to fall to one side or the other, with Autistic traits, or actually ASD.