On average, the gin and tonic cocktail mix contains between 120 and 166 calories per serving. It must be noted, however, that most bars and bartenders in the United States use soda water instead of tonic water. The recommended proportions of a gin and tonic drink are 1:1, 1:2, 1:3 and 2:3, and it is usually served with a wedge of lime slightly squeezed into the cocktail.
Tonic water, which is a major component in gin and tonic, is a bitter-tasting effervescent mixer. Its main ingredient is quinine, which was once used for medical purposes. In the 1700s, quinine was discovered to have the ability to treat or at least prevent the onset of malaria. Since quinine tasted bitter, British officers in India during the 19th century mixed quinine with water, lime, sugar and gin to make it easier to drink.
When it comes to calories, it is worth noting the quinine contains just as much sugar and calories as soda. Some prefer gin and tonic over other cocktails because of the mistaken notion that it contains less calories than other drinks. Since most bars and bartenders in the United States use soda water instead of tonic water, the calorie content of gin and tonic served in the country is between 100 and 140 calories per serving.