Count calories in alcoholic drinks.
Ethanol carries 7 kcal per gram, between carbohydrate and fat, and drinks are sold by volume and strength rather than by mass. Converting is two steps: volume times ABV gives millilitres of pure ethanol, and multiplying by its density of 0.789 g/ml gives grams. Mixers and residual sugar are added separately because they can rival the alcohol itself in a sweet cocktail, while a dry spirit and soda is almost entirely ethanol calories. The units figure uses the UK definition of 10 ml of pure ethanol per unit.
Ethanol energy
kcal from alcohol = serving ml x ABV x 0.789 x 7
Units
UK units = grams of ethanol / 7.89 (one unit is 10 ml of pure alcohol)
These figures are population-average estimates for general planning only and are not medical or dietetic advice. Individual energy and nutrient needs vary widely with body composition, activity, medication and health status. Consult a qualified health professional or registered dietitian before making significant changes to what you eat, and especially if you are pregnant or breastfeeding, are under 18, or have a medical condition or a history of disordered eating.
Residual carbohydrate. A pint of ordinary lager carries roughly 15 to 25 g of unfermented carbohydrate on top of the alcohol, which is what the mixer field is for.
Not quite — a portion is lost as heat, so the effective yield is somewhat under 7 kcal per gram. The larger practical effect is that alcohol suppresses fat oxidation and lowers restraint over food, so the indirect intake often exceeds the direct.
UK guidance is no more than 14 units a week spread over three or more days. Units are a measure of alcohol exposure, not of calories, so a low-calorie drink can still carry high units.