I lived just fine on 16m² for 2½ years, and I had plenty of space for everything I needed to do. I could have 3-4 people over in comfort, any more and we just used the common room or a nearby cafe.
I have lived in smaller as well. But the point is that somewhere around 25 square meters you start taking away functional space. There is a big difference between a 120 cm wide bed and a 70 cm wide bed, or a 90 cm cook top and a 45 cm cook top, or 140 cm wide desk and a 70 cm wide desk. But the same isn't necessarily true as you go up. It is nice to have a bigger kitchen, but the utility diminishes. Or at least per unit of space. While just having a hot plate is likely to decrease ones likelihood of e.g. eating healthy.