The American way is still thinking of a floor as the thing you stand on. We call the first floor that you step on in the building the “first floor” and going up we call the second floor you stand on the “second floor”. Going down to the basement, we call it B1 because its the first floor you step on in the basement amd so on going down.

Europeans call the first floor that you step on the “ground floor” and the second floor that you stand on the “first floor”. Going down, the first floor you hit underground is called "-1 and so on, very similarly to the American system. The naming of floors aboveground doesn’t make logical sense to me, as they should be named for ease of navigation. ~~Telling someone that they need to go up 3 floors and then turn left on the 2nd floor hallway is inherently confusing. ~~

Edit: sorry got that example mixed up.

If you’re building a house I’m Europe and the ask how many floors to build and you say “2”. Are they going to build the floor that sits on the ground and one more or are they going to build the floor that sits on the ground and two more? The naming system lends itself to confusion.