Dry red wines, as opposed to late harvest or fortified wines, have residual sugar of 1 to 3 grams per liter. A six fluid ounce serving contains between roughly one-sixth and one-half of a gram of residual sugar.
The natural sugars in grapes are almost entirely converted to alcohol in the fermentation process of making wine, unless the winemaker intentionally stops the process. Off-dry wines may have ten times as much residual sugar as dry wines, between 10 and 30 grams per liter. At the other end of the sugar spectrum, fortified wines like port, sherry or marsala and late harvest wines may have 150 to 200 grams of residual sugar per liter.