William Poundstone, Photo: Russel Taylor

William Poundstone


How Much Is Enough?

Why ketchup bottles are narrow and yogurt cups are wide.

Posted Jan 13, 2010

In an amusing demonstration of this fact, Brian Wansink and Koert van Ittersum, of Cornell and Georgia Tech, asked student volunteers and professional bartenders to pour out a shot (1.5 ounces) of a simulated liquor. They were instructed to pour carefully, to dispense as close to the exact 1.5 ounces as they could manage. Two types of glasses were used in the experiment: a tall, narrow highball glass and a short, squat tumbler (photo, below). Despite the different shapes, each glass had the same capacity. On average, the students poured 30 percent more "liquor" in the short tumblers than in the tall glasses. The professional mixologists were only a bit more accurate: They poured 21 percent more in the tumblers.
One conclusion: If you're having a party and want to encourage safe driving - or just save on liquor - use tall, narrow glasses. Your guests, or the bartender, will pour less and think it's more.

This result is relevant to the psychology of price, contends marketing consultant Rags Srinivasan in his blog, Iterative Path. As we walk the supermarket aisles, we make a lot of snap decisions. Is that enough ketchup for that price? Is it good deal? These judgments are rarely as exact as they could be. For the most part, we glance at the posted price but don't bother to scrutinize the label for the number of ounces or milliliters. Nor do we look at unit pricing. (Who's got time?) Instead, the purchase decision is based on two datums, the price and an eyeball estimate of volume. Since volume estimates are subject to all sorts of perceptual illusions, they are an important part of psychological marketing.

You've probably seen Discovery Channel shows on creatures that make themselves look bigger to scare off predators. Well marketers do much the same thing with packages. They use perceptual tricks to make packages look bigger. If two energy drinks cost the same, but one can looks bigger, you're likely to try the one with the "bigger" can.
That's why products tend to come in tall, narrow containers. It truly does look like you're getting more for the money. As much as possible, manufacturers try to avoid "tuna can"-shaped containers. There are few exceptions, of course - tuna cans, for one thing. There's generally a good reason for the exceptions. A flaky tuna filet wouldn't fit in a tall can. Pineapple rings need a pineapple-wide can. Guacamole and other dips come in flat containers so that the package presents a chip-friendly surface for serving.

Srinivasan found an ingenious application of the principle at the Tutti Frutti frozen yogurt chain. The chain lets its customers build their own yogurt sundaes and charges 35 cents an ounce, for however much (or little) yogurt and toppings they care to dispense. That flat rate seems eminently sensible, and would appear to preclude any kind of marketing hocus-pocus.
Until you look at the containers, that is. Srinivasan notes that they're wide and short, much like those in Wansink and van Ittersum's experiment. It's likely that most customers will buy more yogurt than they would have with a taller container.