Researchers at Iowa State University and Cornell University found many people pour about 12 percent more than a normal serving without even realizing it.
It's especially true if the glass is wide and the wine is white.
The study found that people do a better job doing a proper pour if the glass is on a table as opposed to holding it in their hand. People also pour more accurately if the wine is red because it's easier to see in a clear glass than white wine.
Researchers say knowing all this can help people control how much alcohol and calories they take in.