My favorite site for looking at calorie counts is the calorie counter on About.com.

Here are the basic pages for the drinks you mentioned:
White table wine: http://caloriecount.about.com/calories-wine-table-white-i14106?size=2
Gin: http://caloriecount.about.com/calories-gin-rum-vodka-whiskey-i14037?size=1
Tonic: http://caloriecount.about.com/calories-tonic-water-i14155?size=1

Here is the count, for one fluid ounce of each:
Wine: 24
Gin: 64
Tonic: 10

But now you have to look at the whole size of the drink. A wine glass is going to be about 4 ounces. So that would be 96 calories.

A gin and tonic will be about one shot of gin (1.5 ounces) and maybe 8 ounces of tonic. Adding that all up, you have 96 + 80 = 176 calories.

So just comparing one drink to another, you're better off with the wine.

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