When are two drinks about the same as two and a-half? When your bartender pours them into short, wide glasses instead of tall skinny ones.
A study says even experienced bartenders tend to pour a splash more alcohol into squat tumblers compared to tall skinny ones.
And lead author Brian Wansink of Cornell University says that splash can add up. Drinking 25 percent more alcohol per drink could affect the ability of partygoers to monitor how much they're consuming.
Wansink suggests bartenders measure the amount of alcohol they pour to be sure.
A researcher not involved with the report says the result of the portion distortion study underscores the need for people to be careful not to underestimate their intake.
The study is published in BMJ, formerly the British Medical Journal.