Pouring a glass of wine is rarely an exact measurement, especially in a social setting. While most people think of a glass as one serving, in reality it could be closer to two or three. Just how much one pours is influenced by a variety of environmental factors, researchers at Iowa State and Cornell universities discovered, and that could have serious consequences when it comes to overconsumption.

In the study, published in Substance Use and Misuse, participants were asked to pour what they considered a normal drink using different types of glasses in various settings. The results show how easy it is to overdo it. Participants poured around 12 percent more wine into a wide glass than a standard one. The same was true when holding a glass while pouring compared to placing the glass on a table.

“People have trouble assessing volumes,” said Laura Smarandescu, an assistant professor of marketing at Iowa State. “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.”

Researchers tested six environmental cues to understand how each influenced the amount poured. 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 influence of a small and large table setting was not as strong.