I have 85m2 for a family of 4 and we are kind of privileged here. as many people have one generation more living under the same roof and less space. We have one bedroom, a kitchen that also serve as dining room, I have a separate office, living room, bedroom, my 2 daughters share the same room (by choice, the "office" used to be destined to be one of my daughter's bedroom). We could easily cram office, living room and parents bedroom into one room without really compromising in term of quality of life.

Sure if you are a kitchen appliances hoarder, you need a 80m2 kitchen already so there is very little room for anything else. If you know how to cook and use your hands everything is much simpler.

Strongly disagree as someone who live in 20m^2 for the past 5 years.

Public space like parks and the walkability of the neighborhood are very important factor for comfortable living in small space. Both of which Japan do very well.

In Oslo, Norway there is a lot of demand for aparments below 40m2 for young couples. 60m2 is considered OK for a family with 2 kids as long as floor plan is reasonable.

Really depends on the person, I lived in 31m² 1DK for two years. I felt I had plenty of room. I especially loved how quickly I could clean up the place and find misplaced items. Finding a lost item was frustrated as I thought how stupid it was to lose an item in a tiny apartment, but it always resolved in about five minutes.

Only as a data point, in Italy the minimal size a house can legally be called a house is 28 sqm, intended for a single, then you add 10 sqm for each additional adult (this is national law, since 1975).

Local laws may increase these mimimum sizes, the tendency is to set the minimum to around 40-45 sqm in many places.

I am living in 25m^2 now for 5 years. It is comfortable.