The average size of a bathroom is 40 square feet, which is just enough area for a pedestal sink, a toilet, and a bathtub. If you want to install a separate shower, you’ll need at least 10 more square feet. Most bathrooms in North American homes constructed prior to 1980 were smaller than 40 square feet.
It is possible to fit a bathroom into a space as little as 40 square feet by
Making do with smaller-than-usual light bulbs
Putting in a shower but not a tub
Changing to a pocket door from a conventional swinging door.
More recently built houses have larger bathrooms and more baths than older residences. A 2,000 square foot home will often feature three bathrooms: a master suite with a spacious bathroom, a second bathroom with a smaller shower and tub, and a half-bath for guests.