Americans use the word "bathroom" to talk about the room where toilets are.

He's in the bathroom.

A more polite word for Americans is "restroom":

Excuse me, where's your restroom?

Canadians say "washroom". British people call it "the loo", I think... I don't know what Australian people call it, but they probably have a different name for it as well. But if you're in the U.S., use "bathroom".