How much is a bowl of cereal? Seems like kind of a silly question. Because a bowl of cereal is the amount of cereal that fits in a bowl. Except that it’s not.

First of all, how big is your bowl? That makes a difference. A deep soup bowl is going to hold a lot more than a shallow fruit or salad bowl. In fact, since most breakfast cereals have a serving size of ½ cup to 1 cup, a “bowl” of cereal should fit in a teacup (before milk). And then you have to factor in the size of the cereal bits themselves, which is why a team of researchers at Penn State crushed up wheat flakes with a rolling pin for a March 2014 study in the Journal of the Academy of Nutrition and Dietetics.

Picture a single Grape-Nut, one Lucky Charm and a solitary Bran Flake. Now imagine a handful of each. You’ll be able to palm a lot more Grape-Nuts, nestled in close and tight, than flakes, which will layer unevenly, with air betwixt and between. The Penn State scientists, led by nutritional sciences professor Barbara Rolls, Ph.D., used this principle to study how much more we eat when we pour out a bowl of small cereal pieces versus whole, fluffy flakes. Spoiler: kind of a lot.

They recruited 41 adults to eat cereal for breakfast once a week for a month. Each participant got an identical allotment of cereal, by weight, from which to serve themselves. The flakes were either whole, or carefully crushed to 80 percent, 60 percent or 40 percent of their regular size. So, they all got the same amount of cereal, but the smaller (more Grape-Nut-like) pieces took up a smaller volume.The volunteers routinely finished their breakfasts, and they all estimated that they had eaten about the same number of calories.

But they hadn’t. When provided with reduced-size flakes, they poured smaller bowls of cereal than when they got whole-flakes, but the servings weighed significantly more and contained about 25 percent more calories. That extra 72 calories is equivalent to eating your breakfast, and then eating another half a bowl of Cinnamon Toast Crunch.

It’s hard enough to estimate what a serving size looks like, let alone when you’re starving and probably late for work. To keep yourself from going overboard first thing in the morning and starting a hyper-/hypoglycemic rollercoaster that could last all day, try buying a breakfast cereal with big flakes and eating out of a modestly sized bowl. Smarter eating, less thinking.