One adult (me) and four kids (14, 12, 10, 8). We are about to move from a 2400sf split-level ranch (with a partially finished basement, extra-deep two-car garage, and two-room shed) to a 1400sf Victorian (with a partially finished attic and tiny one-car garage).
Our current house has three bedrooms -- girls share, boys share, and I have my own room. 800sf of our current house is the lower level, which is a huge recreation room (almost never used) and a canning kitchen/laundry room (used only for laundry). I feel that space is all very underutilized. We just don't need it.
Our new house has three bedrooms but my oldest will be taking over the attic, his brother will have his own room (the small bedroom), the girls will share, and I'll have my own room. We will also have a music room downstairs that will double as a guest room. Somehow the new house feels just as spacious and useable as the old house. We'll see if that is the case.
The old house also has two large bathrooms. The new house has two very small bathrooms. The usefulness is the same but with less square footage (though we will lose the second shower that we now enjoy)
Prior to this house, we lived in a 1100 sf condo (two adults and three kids aged 5, 3, 1). We all shared a bedroom and the second bedroom was our office. There was also a really nice unfinished basement for storage. At the time I thought it was too small because most of our friends lived in McMansions. But now I realize it was a good size for us at the time. We would not have had enough bedrooms once the family bed was behind us though.