Think you know what a healthy portion of soup looks like? When researchers at the University of Chester in England asked people to identify the number of servings in 33 different foods and drinks, participants failed big time—getting only five correct on average. "Restaurant portions have totally skewed our perception," says Kelly Pritchett, PhD, spokesperson for the Academy of Nutrition and Dietetics.

Check out the most troublesome foods, plus the measurement guidelines that can help.