A normal bathroom has a floor area of 40 square feet, which is large enough for a bathtub, sink, and toilet. If a freestanding shower is added, at least 10 additional square feet are required. Before 1980, bathrooms in most North American homes were 40 square feet or smaller.
In a room less than 40 square feet, a bathroom can be installed by:
Using fixtures that are smaller than usual
putting in a shower but removing the bathtub
switching to a pocket door from a swinging door.
Houses that were built more recently have bathrooms that are larger and have more baths. For a total of two and a half bathrooms in a normal 2,000 square foot home, there will be a huge master bathroom, a smaller second bathroom, and a powder room.