Not quite. You are in the kitchen or bedroom... (i køkkenet/ soveværelset...) but "på badeværelset" on the bathroom. The bathroom is the exeption! If you are describing the action of going to the bathroom (as a physical location): "jeg går på badeværelset" or "jeg går ud på badeværelset" but going into another room, it would be "ind i". If shouting from the bathroom, it could be either "jeg er herude" or "jeg er herinde" - but the "correct" option is a matter of personal opinion. Leaving the bathroom, it is "ud af badeværelset".
Other uses of "på" (such as "hvad hedder der på dansk") are not really comparable to the use of prepositions in the pure physical sense.
Once i saw a tiny flat, where entrance, kitchen , toilet and shower were all in one. In big towns, where the rent for flats is realy expensive, many students and other "simple people" are living in such small spaces. Then, when you wash dishes, your cups are actually drying up in the bathroom.. :)