There is also the matter of toppings. You can have traditional like four seasons, margherita, or you can have bbq chicken with eggs and potato topping.
14" is closer to medium size, which depending on earlier meals may just about satisfy two adults, or leave them hungry. With four adults, I can only see it leaving them wanting another pizza.
I just love food. Sometimes hard to stop eating. Especially when I go taiwan or japan. I always put on a lot of weight.
It matches my experience - I can keep myself fully fed for a whole day on a single large pizza. It also reinforces my point - such a pizza might suffice as a dinner for two, but will hardly satisfy more people.
edit: here we just say calories, but it's meant "kilocalories"