A quote attributed to Bill Murray:
Your pizzas might just be bulkier than the rest. I remember Western New York pizza being on the thicker side.
For comparison, something like a frozen Tombstone or Jack’s pizza (which should be the same around the country), I could easily finish an entire pizza in a sitting (and will if I’m the only one eating), but I try to limit myself to 1/3 (which is the serving size listed on frozen pizza, usually.) That said, unless there are 3 people eating with us, I generally end up eating more like at least half of the pizza.
Meanwhile, at a typical Neapolitan pizza place, when I go out with friends, a single pizza is considered a single serving for us. We all order our own. These are 16" pizzas, but the crust is very thin, and the toppings are not heavy.
There is so much variation in what constitutes a “slice of pizza” (could be one of the little corner pieces from a square-cut crispy thin crust cheese pizza, could be a huge slab of a deep dish pizza loaded with toppings) that any answer to the thread title’s question is meaningless without further context.
Absolutely. That’s why I used the frozen pizza example, to see what if we can have some sort of comparison standard. A chain pizza might be another good baseline.
Something like a standard “New York slice” that you’d find throughout the city, one slice will do me fine. Two at the most:
All of them.
Me too. I’m a bigger guy and I’m always slightly ashamed when I eat half (four slices) of a frozen pizza at home. And those are only 12" I think. When I get a large at a real pizza place, it might be more like 2 or 3 slices. And if it’s Giordano’s or Lou Malnati’s deep dish, two slices of their small pizza is more than enough.
I think people in this thread might all be referring to different sized pies, though.
No need to feel guilty. For a typical frozen pizza, a serving size is 1/4 - 1/3 pizza. At most, you’re eating two servings, and serving sizes tend to be on the conservative side. I’m surprised half a frozen pizza is particularly filling to a big guy.
Sometimes I’ll get a couple of DiGiorno “thin and crispy” pizzas, cook them and then flip one on top of the other. Then cut into slices…double the toppings in every bite!
My appetite has diminished with age. I used to eat an entire large pizza with several toppings. Now it’s 3-4 slices with one topping and I’m stuffed. Same with tacos: down from six or seven to two. Sad.
Is my wife there? If she is, I’ll eat 4 slices of a typical take-out pizza. If not, I will eat the whole thing even if I have to keep going back over the course of a few hours.
All of them if I’m alone. If I happen to have a second pizza, that one too.
All of them. If there’s pizza, I will eat it until there is none left. Pizza seems to be the one food that doesn’t exhaust my taste buds - the last slice tastes as good as the first slice, and I will keep eating it until there is no more to eat. This is why I prefer thin crust. It doesn’t fill me up as quickly, so I can more easily eat more pizza.
Of course, I frequently regret this over the subsequent 24 hours, but it’s heaven while I’m doing it 
Ever since I started watching my weight, I try to limit myself to 1/4 of an 18" pizza (what I call 81 “pizza units,” each of which is PI/4 square inches), 3/8 of a 14" (73.5), or half of a 12-inch (72). I can eat about twice that much at once.
After all, somebody has to eat all of that pepperoni, sausage, extra cheese, and pineapple pizza; no one else seems to want to touch it…
If I’m being good, about a 1/4 of a large.
However, due to early training by a grandmother who insisted that all the food should be eaten (to ensure good weather) (and then would cook more because if it is all gone someone must still be hungry) and the appetite control of a Black Lab, I occasionally discover I’ve eaten the whole thing (and I can believe it).
Generally a whole pizza, though the pizza is a medium (or even small, but not personal pan). Pizza is not very filling.
I’ll eat the whole of a medium pizza and half or more of a large pizza.
Easily 4 slices, maybe 6. Nom.
Any sized pizza can be a personal pizza if you believe in yourself.
You have to specify the diameter of the (presumed round) pizza.
In NYC and environs, a round pizza that is sold by the slice has 8 slices cut from an 18" diameter pie, but I think in many parts of the country a “large” pie (largest) is 16" in diameter, which is about 21% smaller (a 64/81 ratio). So 3 regular slices would be 4 of those slices.
And if you’re talking about a 12" pie, that’s about 3-1/2 regular slices in toto.
I have definitely eaten 3-4 slices regularly, and once as many as 6.
I get the smallest size available, and prefer to do so on days I forgot to eat lunch so I’m extra hungry. In those circumstances I will eat the whole thing, which is four slices.
A medium-to-large would be six or eight slices respectively (probably) and I’d only eat half or quarter of those. I am not a big eater anyway. My portions are generally small-to-medium if I have a choice.