For most people, making a Gin & Tonic means adding ice to a glass, free-pouring some gin, and adding some tonic to taste (bonus for stirring). While building in the glass this way is completely fine, especially when at a backyard barbecue or house party, measuring out your ingredients will result in a more balanced and consistent drink for you and your guests.
The general proportions for a classic G&T are two ounces of your preferred gin to four ounces of quality tonic, over ice. Using this 1-2 ratio as you size up or down will ensure that the drink is always in balance. Now just add your favorite garnish — be it lime, cucumber, herbs or whatever else your heart desires — stir, and enjoy.
Though the G&T may seem like a simple two-ingredient cocktail, its simple balance is what makes it such a timeless tipple.