Beside you're atheist if you don't believe in a god.
Or an agnoticist. Or a nontheist.
I wish people would quit wrongly thinking Agnosticism excluded Atheism when they are both a single position that often are adopted alongside the other. While there are people who claim to be "Agnostic" while referring to a ridiculous "can't know anything" position it always ends up being extremely selective in its application and as such is more of a tepid excuse than any real belief. Agnosticism itself, as it was originally conceived, is the position that we should ignore all argument over the existence of things which cannot be proven and stick to what we can know within an observable universe.
Also,
nontheism IS
atheism. There is only confusion because many of the people who self-identify as Atheist have been too stubborn to switch to a more accurate definition of their beliefs (instead of a single position) and butcher our language because they've become attached to the label. Admittedly I like the whole scarlet letter thing that can be done with 'A'theist, but keeping to the inaccurate label is harming the discourse. For example: See a few pages back where a single position somehow became "a belief system". *facepalm*
The different viewpoints of non-theists are too disparate and based on too limited a point to become any truly cohesive group. I guess that's also why most identify as Atheist since all that unites us is a lack of belief in whatever a divine being is supposed to be.