COVID-19 Outbreak (Update: More than 2.9M cases and 132,313 deaths in US)

That's based on an antibody test done at random, but still a statistical sampling. It's an estimate at this point.
It's also based on antibody tests that Roche CEO says is only a little bit statistically better than chance. Unfortunately the antibody tests still need a lot of work and some of the companies shipping them out knowing just how inaccurate they are need to burn in hell.