The first time I tried to order pizza delivery in Singapore, I asked my friends, "So, how big are the pizzas here?" The answer left me stumped: "Small is six slices and large is eight slices." I retorted that I could easily slice a 6cm pizza into 16 slices and that wouldn't feed us any more than their large pizza. They looked at me kind of funny.
Would it not be more useful to size a pizza in terms of diameter, not number of slices or how many people its supposed to feed? As you point out, a 6cm diameter pizza can be sliced into 16 pieces, but also some people just naturally eat more than others anyway.
It definitely doesn't need to be a big crowd like that. 8 slices, maybe 3 or 4 people if it's a full meal (2 slices / person is probably typical). Leftover slices are good the next day too.
