How much privately money can you steal before it becomes a federal case?

It doesn't scale that way.





Violations of federal criminal laws are federal cases.


Violations of federal statutes are federal civil cases.





Theft is usually a state criminal matter, subject to state laws-- and whatever the amount, it's usually handed by the state courts.





If something is a crime under both state and federal laws, then you can be prosecuted under either or both -- if something is only a violation of one set of laws, then you can only be prosecuted under that set of laws.How much privately money can you steal before it becomes a federal case?
There is no set limit. The amount you steal does not matter, it is the way you still that matters/.