How many atheists and agnostics are in the USA?

Currently, atheists in the USA are estimated to be between a few percent (5% or so) to 21%, but, no one can be certain. As a group atheists are "despised" in most parts of that country and tend not to indicate their status in general activities in their communities, or on census or polls.

As for agnostics, since anyone who has doubts could be in that category, the number is even higher to pin down.