These places are actually 9 square meters, including kitchen and bathroom. Typically, the “kitchen” is a hole in the wall which is barely big enough to use to prepare instant ramen, and the bathroom/toilet/shower are combined into a small plastic cube-like room called a “unit bath”.

The catch is that there is a loft which doesn’t count towards the square meterage.

In contrast, an 18sqm place can have a kitchen with two burners where you can actually prepare food, a door between the kitchen and your bedroom so you don’t stink the place up while cooking, and can even have separate rooms for the toilet and sink. A lot of people I've met consider this pretty luxurious, at least in central Tokyo.