It really is impossible to say for sure, for a number of reasons. Firstly, the definition of pedophilia makes it hard to pin down exact figures. Is a 19 year old who dates a 15 year old a pedophile? What about a 73 year old who dates a 16 year old (this is legal in many countries)?

Secondly, a person is unlikely to self-identify as a pedophile, for obvious reasons. And it could be that there are many people with only very slight pedophilic urges, who can suppress these urges, and so they never come to light.

Nevertheless, there have been some attempts at estimating the prevalence of pedophilia. The most notable of these attempts was a paper two years ago in the Annual Review of Clinical Psychology which gave 3% as a reasonable figure.

If we say only people 16 or older are capable of being pedophiles, this gives us roughly 150 million pedophiles in the world.

Note though, that the potential for error in this figure is very great, for the reasons given before. It is quite possible that the number is as low as 40 million, or as high as 400 million. It's definitely around that range though.