Wait. I am pretty sure that i live in America, and here the buildings start at zero. 012 denotes room 12 on floor zero. Room 112 is the first floor room 12 and so on.
Room 112 is on ground level at every hotel I can remember, including on a trip last month. Well, it would have been on the ground level but that floor is all lobby and conference rooms so the lowest toom number was 201 and was on the second floor.
Previous buildings with rooms on the ground level were the 100s.
The building i am in right now has the elevator list the ground floor as G and the next floor up as 1. I can see that there is really no consistency. In buildings that have the ground floor as 1…. Are their basements listed as 0? It can’t be G for sure. Or do they skip right to -1?
You just triggered a flashback about a weird parking garage that had Ground between P1 and P2 so that it would line up with the hotel's Ground floor!
It went:
P3
P2
Ground
P1
Now that you mention the slopes, I do have a fuzzy recollection of a building on a slope having a separate Ground floor from the numbered floors for street level access. 1st floor was the main lobby.
I can't think of one on flat ground ever having separate Ground and 1st floors though.
I've seen B and SB (basement and subbasement) on elevator buttons. Generally those are floors that the public isn't allowed to go to and I never had the right key to activate them so I don't know what was there.
I've also seen B1 B2 B3 B4 B5 for different basement levels, though I don't remember which was on top. Those were all parking levels though so no rooms were numbered.
Usually I’ve seen rooms starting with zero as a basement level, although due to terrain (such as being on a hillside) there could still be direct access to the outside ground. This is especially the case in residential/apartment buildings where windows and direct emergency egress is legally required. Things get wacky when the terrain around a building is not uniformly flat. It can be even weirder in big cities like New York where there might be an entrance at the street level but the hotel reception is up a level because the entrance to a parking garage is at the street level, then above the lobby level there’s maybe a mezzanine level with conference rooms, and then above that is the floor where rooms start and while an American might call that floor 4 or a European would call it floor 3, it might be labeled in the elevator as floor 1, 2, 3, or 4.
The things I have always seen as consistent in the US is whatever number a hotel room starts with is the number you press in the elevator. If you’re in room 647 press floor 6; if you’re in room 1232 press floor 12. Also, whatever level has a star ⭐️ in the elevator is the floor they consider the level with the main entrance. You’ll find the reception/front desk there and it should be obvious where to go for a taxi. It might not be the level to go out if you’ve parked a car, though, especially if the hotel has a parking garage.