FRENCH MADE - A sugar thermometer is used to measure temperatures of up to 220 degrees Celsius. It has a long, skinny shape that is commonly used when making hard and soft candy, like toffee, fudge, brittle, praline, and many more. These candies all start with a common ingredient, which is sugar that is then boiled to a specific stage, such as hard crack or softball.The key to cooking it perfectly is by knowing the exact temperature of the sugar.