How much can I contribute to my solo 401k this year?

[Dan Rudolph]

My wife and I are the sole proprietors of the business that that sponsors our solo 401k (unincorporated sole proprietorship).  That business will probably make a total of $30K in 2018.  I understand that this calculates to a maximum contribution of $27,880.

However, does this mean that:

1. I can contribute $27,880 if my wife contributes nothing?
2. I can contribute only $27,880 / 2 = $13,940 regardless of what my wife does?
3. We can *both* contribute $27,880?

Thanks for any help you can provide.