A standard glass of red wine, poured at the restaurant standard of 5 fluid ounces (150 ml), contains approximately 125 calories. However, this is a baseline average. The exact caloric content of your wine is dictated by two major factors: the alcohol by volume (ABV) percentage and the amount of residual sugar left after fermentation.

Alcohol is highly calorie-dense. While carbohydrates and proteins provide 4 calories per gram, pure alcohol provides 7 calories per gram. Therefore, a robust red wine with a high alcohol content—such as a 15% ABV Zinfandel or Shiraz—can pack up to 160 calories per 5-ounce pour. A lighter red, like a 12% ABV Pinot Noir, sits closer to 115 calories.

Most dry red wines contain very little sugar (less than 1-2 grams per glass), meaning almost all of the calories are derived from the alcohol itself. Sweet dessert wines, like Port, have significantly more residual sugar and higher alcohol, pushing a small 3-ounce pour well past 150 calories.

The body processes liquid calories from alcohol differently than calories from food. Because the body recognizes alcohol as a toxin, the liver prioritizes metabolizing the alcohol before it processes other nutrients. This temporary pause in normal metabolic function means that foods consumed alongside alcohol are more likely to be stored as fat.

Despite its empty calories, red wine is famous for containing resveratrol, a powerful antioxidant found in the skins of red grapes. Moderate consumption has been correlated with certain cardiovascular benefits and an increase in HDL ("good") cholesterol. However, health professionals stress that these benefits do not outweigh the risks if consumption exceeds moderation.

If you are tracking calories, it is crucial to measure your pours at home. A standard wine glass is large enough to comfortably hold 10 to 12 ounces of liquid. Filling the glass halfway can inadvertently double your calorie intake to 250 calories per "glass."