MONDAY, Sept. 30 (HealthDay News) -- You may be serving wine with a heavier hand than you believe: The size, shape and location of a wine glass can affect how much you pour into the glass, according to a new study.

Most people think of a glass as just one serving, but it could be closer to two or three, which means that it can be easy to consume more than you think, the researchers at Iowa State and Cornell universities noted.

The investigators asked study participants to pour what they considered a normal serving of wine into different glasses. The participants poured about 12 percent more wine into a wide glass than a standard one, and the same was true when they held a glass while pouring instead of placing the glass on a table.

The contrast between the glass and color of the wine also made a significant difference. For example, when pouring white wine into a clear glass, participants poured 9 percent more than pouring red, which had a greater contrast to the glass.

The study was published online Sept. 12 in the journal Substance Use and Misuse.

"People have trouble assessing volumes," study co-author Laura Smarandescu, an assistant professor of marketing at Iowa State, said in a Cornell news release. "They tend to focus more on the vertical than the horizontal measures. That's why people tend to drink less when they drink from a narrow glass, because they think they're drinking more."

A standard serving of wine is 5 ounces, according to the U.S. National Institute on Alcohol Abuse and Alcoholism. But it's easy to lose track of how many servings you've actually had if you are pouring more than you realize, said study co-author Douglas Walker, an assistant professor of marketing at Iowa State.

"If you ask someone how much they drink and they report it in a number of servings, for a self-pour that's just not telling the whole story. One person's two is totally different than another person's two," Walker said in the news release. "Participants in the study were asked to pour the same amount at each setting, but they just couldn't tell the difference."

So how do you keep a handle on how much wine you serve and consume?

"If you want to pour and drink less wine, stick to the narrow wine glasses and only pour if your glass is on the table or counter and not in your hand -- in either case you'll pour about 9 to 12 percent less," study co-author Brian Wansink, director of the Food and Brand Lab at Cornell, said in the release.

More information

The U.S. National Institute on Alcohol Abuse and Alcoholism has more about what constitutes a standard drink.