For me, it is simply “bathroom”.
It does vary on circumstance-
At home I say bathroom but at work or at someone’s house or at a restaurant I’ll say restroom or ladies room.
The “loo”.
+1 (or in less polite company “bog” or “kharzi”)
Due to many years of hanging out with an Irish lass, I refer to it as the loo.
ETA: loo + 2
I assume that for the OP, “bathroom” does not mean a room containing a bath, but a room containing one or more toilets. My most common term for it is probably the “loo”, but when in the U.S. seeking directions to the nearest men’s toilets I’ll ask for the “men’s room” to avoid ambiguity.
The common term in Canada is “washroom.”
Bathroom in most casual situations, which is 95% of the time.
Otherwise, restroom.
I don’t believe there’d be any confusion whatsoever in using “toilets” here in the US. It’s not as commonly used over “bathroom” or “restroom”, but I wouldn’t even flinch if someone asked me where the “toilets” were.
Most Americans know what the “loo” is too. But I can see more confusion over that one, depending on the people.
Bathroom = the place with a bath/shower … not necessarily a toilet
Toilet = definitely has a toilet but may also include bath etc
More common in Australia to ask where the toilet is … if you asked in my house where the bathroom was - there is no toilet in there so you might be disappointed!
Huh.
I’ve seen bathrooms with a bathtub/shower and a toilet, and “half-baths” (to use realtor parlance) with only a toilet and a sink, but I don’t think I’ve ever seen a bathroom with a tub/shower but no toilet in it in the US.
Sometimes I may ask “Where is the potty”. But I am a little odd.
Never heard of loo. Is it pronounced lu or low?
I’ve always been partial to “the can” or “the head” — they’re colloquial, yet innocent enough that you can get away with using them in mixed company.
Of course it goes without saying (though I’m saying it anyway) that you have to have a pretty good feel for the collective stick-assedness of the room before dropping a “Steve’ll be here in a minute; he had to hit the head” or “Pardon, where’s the can?”, but in the right situation, it can serve as a tension breaker or a clear indication that you’re not standing too strictly on formalities.
Like the name Lou (lu).
Well, the room in a house with a toilet is called the bathroom, in my experience. A public toilet would be called a washroom, though.
Ok, I gotta 'fess up. I don’t say this. ^^ I say bathroom; restroom occasionally. I just had the thought “I go tinkle in the loo”-with my pinkie in the air-pop in my head when I read this OP. 
I’ve seen bathrooms without a toilet in Australia. They generally are in houses where the toilet was in a separate room from the house – like this one, which is in rural Georgia in the U.S., and closely associated with a former President. The toilet would not have been connected to the sewer, but either it was connected to a septic tank or the effluent was collected by a night soil collector (which was not the most glamorous of occupations).
Ahh, the quintessential “outhouse”. With the crescent moon on the door and everything.
Heh, that’s where President Carter pooped.
But that’s the way you said it at the Dopefest… Even your voice took on a proper elderly British woman accent!
There’s an episode of Comic Strip Presents, I think it’s Fistful of Traveller’s Cheques, where Nigel Planer’s character is desperate to go and yells at the Spanish locals “Where is el boggo?”
So I call it “el boggo”. Not really, I usually call it the toilet or loo.