I don't know why people here seem to have not bothered even trying to find any possible info on the matter, and just declare it unknowable. There is some information, not a lot, but enough to discredit the people here who for some reason insist on ridiculously lowballing the number and calling anything else delusion. Again, I don't why underestimating is considered by others here as the more "sensible", and "intelligent" position, but I get the feeling this insistence isn't based on pure objectivity like they claim.
Anyway, as far as the U.S. goes, there is some data that we have, and I've tried to piece together the little bit there is to estimate something. I'll copy a post I made about it on another site here.
In a large, national poll on attitudes to interracial dating done back in 2005, they asked people about their dating history. 24% of white women admitted to having dated a black man in there.
https://news.gallup.com/poll/19033/Most-Americans-Approve-Interracial-Dating.aspx
A similar study of students in California from 2000 found that 28% had dated a black guy.
https://www.researchgate.net/public...Among_American_College_Students_in_California
I'd take the national poll as being a better measure of things as it had more people, and a wider variety of women.
But that's just dating, what about adding in casual sex? It's definitely more likely that a white woman would fuck a black guy than date one. So there is this other study about black and white women's reaction to watching porn. The main point of the study is not the focus here, but the part where they gathered information on the women participant's dating and sexual history are. In it, the white women admitted in group 1 that 33.3% had dated interracial while 80.8% had had interracial sex. In group 2, 24.3% had dated interracially and 77.8 had had interracial sex. Of course this didn't just mean black men. But it gives an idea of how much more likely interracial sex is compared to dating.
https://sci-hub.yncjkj.com/10.1300/j514v19n02_02
If we're using that data collected from the two groups we got, it averages out that interracial sex was 2.8x more common than interracial dating. So if we apply that to the poll results of 24% of white women having dated a black man, that would mean that 67% have dated or slept with one. Of course that poll is also from almost 20 years ago. Interracial relations are much more accepted and common now than before. If we play it safe and apply just a modest increase to the old dating data, and put it to 30% instead of 24 , then perhaps you could say that around 85% of women in the current year have possibly slept with a black guy.
That's the best I can guess.