that's all she wrote

that's about the size of it

That is the situation; that is how it is.

that's done it

Used to announce a successful solution to a problem.

that's just me

Indicates the expression of a personal opinion, but often used ironically as an understatement.

that's saying something

Said of something that has an even greater impact or effect than what is readily apparent, considering the context.

that's that

There is nothing more to say or to do concerning the matter and is not up for discussion or debate.

that's that on that

Synonym of that's that; there is nothing more to say or to do concerning the matter and is not up for discussion or debate.

that's the thing

Used to seize on a point and highlight its comparative importance, especially as a refutation or negation to a statement made by another speaker.

that's the ticket

That's just right; that's just what is needed.