Use tall narrow glasses. See why below.
William Poundstone, author of the excellent Fortune’s Formula: The Untold Story of the Scientific Betting System That Beat the Casinos and Wall Street, writes:
In an amusing experiment, 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.