Today I’m going to give you a juicy investigative piece on … wait for it … pizza.

I was in a hurry the other day, and my local pizzeria had just opened. The guy behind the counter had some pies already made and sitting on display. I wasn’t going to eat the pizza right away so, instead of having to wait for a freshly made one, I suggested that he give me one of the pies behind the glass.

He wouldn’t do it.

I assured him that I didn’t need the pizza hot since I was going to freeze it anyway. He still wouldn’t give in. And then he told me the secret: That pie on display was larger than the ones he gives customers to take home.

Jeez! I thought. My hometown pizzeria was scamming me.

Eventually the pizza guy gave me the larger pie and, guess what, it didn’t fit into the standard-size box — a sure sign that I had uncovered a deceitful practice.

Shame on him. But I soon learned that this was, if not a universal practice, then at least a very, very common one. My colleagues and I, energized by the dark underbelly of pizza-making that I had discovered, called around and found that my pie guy was not alone.

In fact, everybody seems to hand out short pies to takeout customers.

I was in a pizzeria on Staten Island recently when one of the workers yelled out that they were running out of “house pies.” I asked, “Are those the larger pizzas that you sell by the piece?”

Without the least bit of embarrassment, the worker confirmed my suspicion. The people who were waiting for their orders all gasped in disgust and amazement at my finding.

Here are the piping-hot details. Those pizzas you take home are 16 inches in diameter. The ones that are sold by the slice are 20 inches. Let’s say a full pizza costs $15, which we think is the typical price these days. And a slice of pizza goes for $2.50, also standard around Manhattan and in the ’burbs.

There are typically eight pieces to a pie. So a pie that is sold by the slice is worth $20 — or eight pieces times $2.50 if you want to see the math.

The 16-inch pie is just under 201 square inches in size. The 20-inch pie is 314 square inches. So one slice of the eight-piece, 16-inch pie is 25.12 square inches. And a piece of the 20-inch pie is 39.25 square inches.

With those numbers, you are paying 7 cents per square inch for the smaller pie and only 6 cents per square inch for the larger one. (Those are rounded just like the pies.)

So, to my surprise and maybe yours, it’s typically a better bargain to go into the pizzeria and order eight single slices of pizza rather than a full pie. To be precise (or as precise as you can get with these “typical” numbers), you’d be getting 56 percent more pizza for only 33 percent more cost.

Of course, there are other considerations. Sausage and salami are more expensive as toppings than mushrooms, for instance. Anything you add to the pies changes my calculations — but not the underlying fact that you are still getting less pizza for the money if you order a takeout pie.

And don’t even get me started on those dollar-a-slice pizza places. You can do that math yourself.

What’s my conclusion from all of this? I eat way too much pizza.