A calorie is the unit measurement (pre-SI) of energy. Calorie is derived from the Latin word “calor” (heat). In most fields, the “calorie” has been replaced by the joule, the SI unit of energy. Calorie is often described as the amount of energy obtained from food. The Calorie calculator is a useful tool to figure out how many calories you need to consume per day to maintain your current weight, increase your weight or lose weight.