I just learned the phrase “in one sitting” means during one continuous period when you are sitting in a chair.
The example is I sat down and read the whole book in one sitting.
So is it okay to say:
- I ate the cake in one sitting?
- I climbed to the sixth floor in one sitting?
Better is: I read the whole book in one sitting. (You don’t need to say that you sat down and read it in one sitting. That would be redundant.)
Also, it typically needs to be something that you did in its entirety: I ate the entire cake in one sitting. (That’s the whole idea behind doing it in one sitting.)
Even though you don’t necessarily have to literally be sitting the entire time (if you took a break and went to the kitchen or to the bathroom, for example, no one is going to say, “well, you didn’t really do it in one sitting then”), it still has to be some kind of activity that you do while sitting. You can’t say that you climbed anywhere “in one sitting.” That doesn’t jibe with the expression. In that situation you would say something like: I climbed all the way to the sixth floor without stopping to rest.