Red wines typically have slightly lower amounts of residual sugar than white wines. So if you are strictly comparing apples to apples, the calories in red wines will often be a little lower than those found in a glass of white wine. Although, most nutrition charts don't split hairs on residual sugar content and allow for both red and white wines to weigh in at 25 calories per ounce of wine.
While white wines often retain more sugar in the fermentation process, the additional caloric burden is quite negligible, unless it is a sweet dessert wine or ice wine. For your typical Chardonnay, Sauvignon Blanc, Pinot Grigio and the like, you can still count on 25 calories per ounce of white wine.
Wine and Calories, the Bottom Line
Just like all other aspects of calorie-counting, it's the portion size that really matters. Most nutrition charts have a caloric content that is based on a 4 ounce glass of wine (literally a half cup), yet most wine glasses are filled with 5-6 ounces of wine, making a realistic glass of wine more like 125-150 calories per "real world" serving.
Search the USDA National Nutrient Database for the Specific Calories by Wine Varietal For some, knowing that there are approximately 25 calories in an ounce of wine, is just not enough. They want to know exactly how many calories are in their Merlot or Sauvignon Blanc. For those detailed dieters, there's the official USDA National Nutrient Database wine calorie count, broked out by wine varietals. Check out the National Nutrient Database for yourself and find all you need to now about wine calories.