The number of calories in vanilla iced coffee at Sonic varies depending on the size. A small vanilla iced coffee has approximately 170 calories. A medium size contains around 230 calories, while a large size has about 300 calories. It's important to note that these calorie counts may change if additional ingredients, such as cream or sugar, are added. To enjoy a lower-calorie option, you can choose to have the vanilla iced coffee made with skim milk or request it without any additional sweeteners. Keep in mind that these numbers are estimates and may vary slightly based on preparation methods.